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Sensitive assays of histidase activity were used to follow the production of this enzyme as directed by a gene newly introduced into cells of Bacillus subtilis by transformation. Histidase activity can be detected in histidase-negative recipient cells within 1 hr after the addition of deoxyribonucleic acid extracted from histidase-positive donors. Enzyme production continues for one to two additional hours and then ceases. Histidase production in the transformed cells is fully sensitive to catabolite repression. Catabolite repression is rapidly established after transformation of recipient cells that are resistant to this form of regulation.

Nuclear and nucleolar RNA of rat liver labeled with [6- 14 C]orotic acid or [ 32 P]-orthophosphate were separated into sedimentation classes of 18-S, 28-S, 35-S, 45-S and 55-S nuclear RNA and 28-S, 35-S and 45-S nucleolar RNA. After purification of each class of RNA, the distribution of radioactivity was determined in the oligonucleotides obtained by hydrolysis with pancreatic ribonuclease after they were separated by a mapping technique. For nucleolar 28-S, 35-S and 45-S RNA, no marked differences were found for distribution of either isotope in the oligonucleotides. The distributions of isotope in oligonucleotides of nuclear 28-S and 35-S RNA were very similar; these oligonucleotide distributions differed from those of the 18-S and 55-S nuclear RNA which were also very similar. On the basis of the distribution of isotope in the oligonucleotides, liver nuclear 28-S, 35-S and 45-S RNA appear to be mixtures of the nucleolar, GC-rich RNA and the cosedimenting AU-rich RNA. The data are interpreted by the hypothesis that 28-S, 35-S and 45-S nucleolar ribosomal precursor RNA have very similar primary structures. Since 18-S nuclear RNA has a very similar distribution of isotope in oligonucleotides to that of 55-S nuclear RNA, the latter may be a precursor of nuclear 18-S RNA.

The present paper outlined the evidence for the specificity of the alterations observed in the neoplastic liver in terms of their ability to provide an integrated system of quantitative and qualitative discriminants that can clearly distinguish the neoplastic liver from the rapidly growing fetal, newborn, adult, or regenerating liver. This examination of the specificity of the imbalance of enzymes and metabolic pathways in hepatomas is based also on studies on the ordered nature of the biochemical pattern in hepatomas of different growth rates that has been documented in earlier publications. The evidence leads to the conclusion that in the model system of hepatomas of different growth rates and in a control system of rapidly growing differentiating and regenerating liver there is a biochemical pattern that is ordered and specific to neoplasia. The results examined in this paper deal with key enzymes and metabolic pathways in carbohydrate, pyrimidine, DNA and ornithine metabolism. Similar considerations should apply to other biological systems and control mechanisms. The application of the conceptual and experimental approaches of the molecular correlation concept to the cyclic AMP system is reported elsewhere.

The dominant tomato mutant 'Curl' differs from normal plants in several striking respects including the following: misshapen laminar structures such as leaves, sepals, and petals; stunted petiole and rachis; and persistent growth of blade and stem tissue from the adaxial surface of the rachis. These tissues as well as others which appear morphologically normal show gross histological abnormalities. Also evident in sections of mutant tissue is the appearance of areas containing numerous crystalline inclusions and a lack of bodies showing a stainable starch reaction in palisade and mesophyll of leaves and in endodermis and pith cells of the stem. ONE SUCCESSFUL approach to the study of the functioning of genetic material has involved the use of mutants to investigate the control of the enzymes of lactose utilization by the haploid Escherichia coli cell (Jacob and Monod, 1961). To extend our understanding of the control of genetic information and of the development of form from this information to diploid organisms, single gene mutants which produce marked morphological characteristics may be useful experimental materials. In a study of the expression of a gene producing a distinctive phenotype, at least two sequential components can be theoretically delineated (modified from Ebert and Kaighn, 1966): differentiation and morphogenesis. Differentiation is the appearance of change in the metabolism of cellular molecules such as nucleic acids or proteins as a consequence of the expression of different segments of the cell's one-dimensional DNA sequence. Morphogenesis includes the phenomenon of shaping the three-dimensional structures of cells by folding and aggregation of one-dimensional gene products which leads eventually to externally visible, three-dimensional phenotypes. Recognizing these two aspects of gene expression, a genetic study of the control of the expression of hereditary information manifested morphologically would then involve first, an initial characterization of the morphology and histology of normal and mutant; second, identification of differences at the level of molecules; and third, evidence for the mechanism of the externally visible effect. Higher plants are well-suited for studies of differentiation and morphogenesis, particularly because of their permanently embryonic regions, I Received for publication 19 October 1970. Submitted as part of a doctoral dissertation in the Genetics Department, Univ. of Calif., Davis. Supported in part by NIH Training Grant GM 701. 2 Present address: Biology Department, Occidental College, Los Angeles, Calif. known as meristems (Stebbins, 1965). Obvious mutant morphological features may be first seen as conspicuous differences between mutant and normal tissues in meristem differentiation patterns. For example, Stebbins (1965) and Stebbins and Yagil (1966), in studying the action of the hooded gene in barley, have shown that an increase in the nucleic acid metabolism of cells in a specific region of the mutant meristem is correlated with an increased tempo of mitosis and change in division patterns, resulting in an obvious morphological feature in the mutant. Since a characteristic morphological form may be generated through growth in the absence of cell division (Haber and Foard, 1964), careful observations of patterns of change in cellular constituents (not only nucleic acids) can be important in understanding the action of genes in the development of form. In the investigation described in this paper the dominant tomato leaf mutant 'Curl' was studied morphologically and histologically as the groundwork for further exploration into biochemical determinants in the differentiation and morphogenesis of leaves. 'Curl' is a spontaneous mutant of Lycopersicon esculentum Mill. which originated as an abnormal branch on an otherwise normal plant of the 'Stokesdale' variety of tomato. As described by Young (1955) the leaves of this branch were dwarfed, curled, in rosette bunches, and the two fruits borne by this branch produced 80 % mutant and 20 % normal plants. Upon further selfing and in crosses with other tomato stocks it was found that the mutant is inherited as a dominant and Young proposed the symbol Cu. Rick and Harrison (1959) reported the locus of Cu to be on chromosome 2, close to Wo. MATERIALS AND METHODS-Growinq conditions -Seeds of homozygous 'Curl' (Cu/Cu) as well as seeds of the parent variety, 'Stokesdale' (Cu+/ Cu+), were obtained from Dr. Charles M. Rick

It is now well established that the entire genetic information is con­ served in DNA base s equence. Each cell of the multicellular organism con­ tains the same DNA. In other words, each cell possesses the same genetic information. However, due to the pronounced differences in their protein composition, these cells are quite different in their properties. Thus only part of the genetic information is realized in each cell. The realization of genetic information, or gene expression, consists of a number of steps. The more important steps are: transcription or RNA synthesis, transport of RNA to the sites of protein synthesis, and translation or protein synthesis in ribosomes on the messenger RNA template. At any step of this complex process, some limitation of information may occur and the "information stream" may narrow. As a result, only part of the DNA base sequence is realized in polypeptide chains. The first step of such a limitation process is transcription. A number of papers have appeared to indicate that RNA in different tissues of the same organism is synthesized on different parts of the genome. This has been demonstrated with the aid of the competitive-hy­ bridization technique between DNA and RNA's isolated from different tis­ sues of the same species (1). Thus the question of the mechanism of this limitation of transcription arises. What are the molecular mechanisms of this "switching off" of some DNA molecules from the biosynthesis of messenger RNA (or their "mask­ ing") ? In 1945 the English scientists Stedman & Stedman (2) developed the hypothesis that histones, the bas ic proteins of the cell nuclei, inhibit gene activity in the cell. It should be pointed out that the appearance of histones in evolution takes place at the same time that organisms acquire two other fundamental properties . One of these properties is the separation of the nu­ cleus from the cytoplasm by a membrane. This distinguishes two main groups of organisms : prokaryotes and eukaryotes. Prokaryotes do not con­ tain histones in the nuclei [see for an example (3)]. The second fundamental property, which is especially pronounced in multicellular organisms, is differentiation. Thus the appearance of histones in evolution roughly coincides with the appearance o f a well-defined nucleus (and chromosomes ) and with differentiation. Therefore, one can assume histones to be involved in the organization of chromosomes and in prolonged switching off of genes. This long-term masking of some of the genes may

Before mRNA was discovered it was commonly accepted that ribosomes in cells are specialized for the synthesis of specific proteins. Following the demonstration that the information for the amino acid sequence is, in fact, in the mRNA, ribosomes began to be viewed as non-specific organelles, capable of translating indiscriminately all information brought to them by mRNA. If this concept is true, all the controls of gene expression which must come into action when a cell adapts to new environmental conditions should be exclusively at the level of mRNA synthesis (transcription and maturation). To determine if translation control is at all a possible mechanism for the control of gene expression, it is therefore important to establish whether or not ribosomes are capable of discriminating between mRNAs and of translating preferentially one or another of the mRNAs present in the cytoplasm. This question is of course most relevant for mammalian cells, in which we know that (1) stable mRNAs function for prolonged periods of time (1) and (2) that more mRNA is synthesized in the nucleus than is actually translated on the cytoplasmic polyribosomes (see Scherrer, this volume). Since, however, the mechanism of protein synthesis is known in more detail in E.coli, we have concentrated much of our efforts in studying mRNA discrimination by E.coli ribosomes. Our experiments over the past three years have clearly demonstrated the existence of ribosome-associated protein factors which make the ribosome specialized for specific mRNAs. Recently, we have isolated similar factors from mammalian cells; these results will be presented in the second part of this paper.