The SPOII gene, required for meiotic recombination in Saccharomyces cerevisiae, has been cloned by direct selection for complementation ofthe spolIl-phenotype: lack of meiotic recombination and low spore viability. DNA sequencing indicates that the gene encodes a 398-amino acid protein having a predicted molecular mass of 45.3 kDa. There is no significant similarity between the SPOil protein and other protein sequences, including those from genes known to be involved in DNA recombination or repair. Strains bearing a disruption allele are viable, indicating that SPOil is dispensable for mitotic growth. RNA analyses demonstrate that SPOII produces a 1.5-kilobase transcript that is developmentally regulated and expressed early in the sporulation process.

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Simian virus 40 (SV40) stimulated a host cell antigen in the centriolar region after infection of African green monkey kidney (AGMK) cells. The addition of puromycin and actinomycin D to cells infected with SV40 within 5 h after infection inhibited the stimulation of the host cell antigen, indicating that de novo protein and RNA syntheses that occurred within the first 5 h after infection were essential for the stimulation. Early viable deletion mutants of SV40 with deletions mapping between 0.54 and 0.59 map units on the SV40 genome, d12000, d12001, d12003, d12004, d12005, dl2006, and d12007, did not stimulate the centriolar antigen above the level of uninfected cells. This indicated that an intact, functional small-t protein was essential for the SV40-mediated stimulation of the host cell antigen. Our studies, using cells infected with nondefective adenovirus-SV40 hybrid viruses that lack the small-t gene region of SV40 (Ad2+ND1, Ad2+ND2, Ad2+ND3, Ad2+ND4, and Ad2+ND5), revealed that the lack of small-t gene function of SV40 could be complemented by a gene function of the adenovirus-SV40 hybrid viruses for the centriolar antigen stimulation. Thus, adenovirus 2 has a gene(s) that is analogous to the small-t gene of SV40 for the stimulation of the host cell antigen in AGMK cells.

The correlation between growth conditions and centriolar antigen (Cag) expression in TC7 cells, a subline of African green monkey kidney cells, was studied. TC7 cells became quiescent when their number reached a high cell density, or when serum factors were depleted from media containing a low concentration of fetal bovine serum (FBS). There was a stoichiometric relationship between the concentration of serum present and the number of new cells produced. During proliferation, the projected cell area decreased as a function of cell density with two abrupt transitions. The first transition appeared to be independent of cell-cell contact. However, the second transition seemed to occur mainly as a result of the limitation of the available substratum surface on which the cells could grow. The appearance of Cag in TC7 cells was found to be associated with the cells' growth conditions as well as with the particular phase in cell cycle. In an exponentially growing culture of cells with 10% FBS and in cells that were growth restricted due to a high density (above 2-3 X 10(5) cells/cm2), the incidence of cells with Cag-positive staining was about 10-20%. It increased, however, to about 40-60% at cell densities between 2 X 10(4) cells/cm2 and 1 X 10(5) cells/cm2. The frequency of cells with positive Cag staining was as high as 80% in TC7 cells that were growth restricted by depletion of serum factor(s). Thus, the quiescent states attained by the two different growth restrictions seem to be different in their ability to express Cag. The frequency of Cag could be further increased by stimulating the quiescent cell population by FBS. In mitotically selected TC7 cells, Cag staining appeared about 4 hr after mitosis and about 2-4 hr before the onset of DNA synthesis. Thus, expression of Cag in TC7 cells is related to their growth conditions, and is characteristic of a part of the G1 phase of the cell cycle.