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A mutation in Histone H2A kinase, nhk-1, in 'Drosophila' that leads to female sterility due to defects in the formation of the meiotic chromosomal structures is described. The role of Histone H2A phosphorylation with respect to the histone code hypothesis is analyzed and it is found that Histone H2A is required for acetylation of Histone H3 and Histone H4 in meiosis.

Chromosomes are dynamic structures that are reorganized during the cell cycle to optimize them for distinct functions. SMC and non-SMC condensin proteins associate into complexes that have been implicated in the process of chromosome condensation. The roles of the individual non-SMC subunits of the complex are poorly understood, and mutations in the CAP-G subunit have not been described in metazoans. Here we elucidate a role for dCAP-G in chromosome condensation and cohesion in Drosophila. We illustrate the requirement of dCAP-G for condensation during prophase and prometaphase; however, we find that alternate mechanisms ensure that replicated chromosomes are condensed prior to metaphase. lit contrast, dCAP-G is essential for chromosome condensation in metaphase of single, unreplicated sister chromatids, suggesting that there is an interplay between replicated chromatids and the condensin complex. In the dcap-g mutants, defects in sister-chromatid separation are also observed. Chromatid arms fail to resolve in prophase and are unable to separate at anaphase, whereas sister centromeres show aberrant separation in metaphase and successfully move to spindle poles at anaphase. We also identified a role for dCAP-G during interphase in regulating heterochromatic gene expression.

Key Words DNA replication, mitosis, checkpoint, differentiation, cell growth Abstract An intriguing aspect of cell cycle regulation is how cell growth and division are coordinated with developmental signals to produce [...]

In this review molecular and physiological basis of endoreplication or endocycles are considered in terms of regulatory mechanisms, control switches, and upstream regulators operating during cell differentiation and growth. Specific examples from insects, mammals, and plants are discussed.

A Drosophila gene, double parked (dup), has been identified. It belongs to a new family of replication proteins conserved from Schizosaccharomyces pombe to humans. DUP seems to function directly in DNA replication. The conserved essential replication protein is colocalized with the origin-recognition complex. It links DNA replication with mitosis and down-regulation of S phase transcripts.

ACE3, an origin of DNA replication control element and Drosophila origin recognition complex (DmORC) are discussed. Through use of in vivo and in vitro approaches, it has been shown that ACE3 and AER-d are DNA-binding sites for DmORC. Likely DmORC DNA-binding specificity controls origin selection. Identifying DmORC-binding sites in vivo probably will be powerful in identifying other Drosophila origins.

Localization of the sister-chromatid cohesin complex is discussed as it occurs on yeast chromosomes in this review article. Topics include delocalization in stages of a meiosis-specific cohesin complex and the relationship between sister-chromatid cohesion and kinetochore behavior. Identification of the cohesin complex and its role at the centromere makes delineation of the molecular mechanism by which cohesion is established and maintained possible.