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Mother-to-child transmission (MTCT) of human immunodeficiency virus type 1 (HIV-1) as described for women with an established infection is, in most cases, associated with the transmission of few maternal variants. This study analysed virus variability in four cases of maternal primary infection occurring during pregnancy and/or breastfeeding. Estimated time of seroconversion was at 4 months of pregnancy for one woman (early seroconversion) and during the last months of pregnancy and/or breastfeeding for the remaining three (late seroconversion). The C2V3 envelope region was analysed in samples of mother–child pairs by molecular cloning and sequencing. Comparisons of nucleotide and amino acid sequences as well as phylogenetic analysis were performed. The results showed low variability in the virus population of both mother and child. Maximum-likelihood analysis showed that, in the early pregnancy seroconversion case, a minor viral variant with further evolution in the child was transmitted, which could indicate a selection event in MTCT or a stochastic event, whereas in the late seroconversion cases, the mother's and child's sequences were intermingled, which is compatible with the transmission of multiple viral variants from the mother's major population. These results could be explained by the less pronounced selective pressure exerted by the immune system in the early stages of the mother's infection, which could play a role in MTCT of HIV-1.

Continuous cultivation of murine L cells infected with lymphocytic choriomeningitis virus strain Armstrong leads to production of L(Arm) cells, which produce a predominantly cell-associated attenuated variant, the L(Arm) virus. The relatively few infectious particles that are released have lost the ability to form plaques on L cells and to cause illness in mice even if inoculated intracerebrally. Based on equal protein M(r)s, antigenicity and protein kinase activity, essentially identical results were obtained for the purified Armstrong and L(Arm) viruses. There was also no difference in production and release of particles with the potential to cause homologous interference. Such particles consisted of two types, one of which was highly susceptible to u.v.-irradiation, the other was highly resistant. In the case of the L(Arm) virus interfering particles, it appears that the u.v.-irradiation-susceptible forms represented infectious virus. Purified L(Arm) virus particles contained considerable quantities of subgenomic forms of (small) S- and (large) L-RNA and their complementary counterparts, which all appeared to be replicated autonomously in an unenriched manner.

Analysis of radioactively labelled and highly purified infectious lymphocytic choriomeningitis (LCM) virus by polyacrylamide gel electrophoresis (PAGE) revealed 12 components which, according to their apparent molecular weight and glycosylation status, were designated as p19, p25, p26, gp35, p38, gp44, gp60, p63, p77, gp85, gp130, and p200. As shown by immunoprecipitation, they all bound to rabbit anti-LCM virus antibodies. Three proteins, namely gp35 (= 'GP-2'), gp44 (= 'GP-1') and p63 (= 'NP'), had previously been described by others as major constituents of the virion. Our results confirm this and suggest that gp60, p77, gp85, and p200 are further distinct structural proteins. In contrast, p25 and p38 appear to be cleavage or degradation products of p63; p19 and p26 seem to belong to gp60, which could be the monomeric form of a dimer, gp130. Peptide mapping by limited proteolysis revealed considerable overlapping of amino acid sequences among the major glycoproteins with one peptide being common to all. From the results of PAGE performed after external labelling of intact virions, we conclude that gp44, gp60, and gp85 (but not gp35) form the surface of the virus envelope. Analytical isoelectric focusing under non-reducing conditions has shown that the major glycoproteins appeared to consist of several components with different isoelectric points.