The high molecular weight cldemon (h-

Cytogenetic abnormalities associated with human papillomavirus (HPV) type 16 were studied using primary human and mouse epidermal keratinocytes. The E7 transforming gene of HPV-16 was found to induce chromosome duplication in epidermal keratinocytes; little or no detectable chromosome disorganization was associated with the function of the E6 gene. These results suggest that the E7 gene-linked cytogenetic effect reflects HPV-16-associated pathogenicity in the early phase of transformation.

Meiosis-deficient mutants of the fission yeast Schizosaccharomyces pombe carrying mei1, mei2, mei3, mei4 and mes1 mutant alleles were characterized by electron microscopy and staining of the nucleus with 4', 6-diamidino-2-phenylindole. Zygotes of either mei1, mei2 or mei3 mutants contained one round nucleus with a single spindle pole body (SPB). These mutants were arrested before premeiotic DNA synthesis. Zygotes of mei4 mutants had one elongated nucleus containing thick electron-dense filaments (linear elements). In the mes1 mutant, the first meiotic division was completed but the SBPs did not duplicate. Modification of the SPB (outer plaque formation) was also blocked and the forespore membrane was not assembled. By haploidization, random spore and tetrad analyses, four essential genes for meiosis (mei2, mei3, mei4 and mes1) were mapped. Gene mei2 was located on chromosome I 14.2 cM distant from ura2. Gene mei3 was linked to ade7 (45.4 cM) on chromosome II. Gene mei4 was linked to cdc2 (0.6 cM) on chromosome II. Gene mes1 was linked to ura3 (25.3 cM) on chromosome I.

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ABSTRACT. Cell extracts of a murine leukemia cell line, Ml, apparently contain three kinds of actin-gelation factors; a filamin-like protein, and 38K-dimer and 105K-dimer proteins. Unlike gelation by the filamin-like protein, gelation by the latter two proteins is inhibited by low concentrations of KC1. Our study of the 38K protein has been reported elsewhere (Takagi, K. et al., J. Biochem. Tokyo 97, 605-616, 1985). We here describe the purification and characterization of the 105K protein.The 105K protein differs from the a-actinin group of proteins in its antigenicity, peptide components and Ca 2+-insensitivity. The saturated binding ratio of the protein to purified skeletal muscle actin is 1 : 8; when this ratio exceeds 1 : 20, gelation takes place. This gelation is inhibited completely by the presence of 25 mM KC1. Electron microscopy revealed that, in the absence of KC1, the 105K protein/actin mixture forms short actin bundles that are accompanied by a meshwork of short single filaments. The presence of 25 mM KC1 did not prevent actin-bundling, but the bundles became longer and the meshwork of short filaments was no longer present.