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The YPT1 gene of the yeast Saccharomyces cerevisiae codes for a guanine nucleotide‐binding protein which is essential for cell viability. Using as hybridization probe cloned yeast YPT1 gene sequences, we have isolated from cDNA libraries prepared from RNA of mouse F9 and C3H10T1/2 cells several overlapping cDNA clones with identical sequence in the regions of overlap. The cDNAs were derived from a gene, designated ypt1, which codes for a protein of 205 amino acids with 71% homology to the yeast YPT1 gene product. Amino acid sequences typical for guanine nucleotide‐binding proteins and characteristic for ypt proteins are perfectly conserved in the mouse ypt1 protein. Two mRNAs of 1600 and 3200 nucleotides, originating from the mouse ypt1 gene and differing in the length of their 3′‐non‐translated region, were identified in mouse F9 cells and in all mouse tissues examined. A monoclonal antibody specifically recognizing the 23.5‐kd yeast YPT1 protein cross‐reacted with a protein of identical size on protein blots of mouse, rat, pig, bovine and human cell lines.

The isolation and characterization of a temperature-sensitive mutant (tsl S 13) of the avian erythroblastosis virus, S13, is described. The temperature-sensitive lesion in tsl S13 was identified as affecting the tyrosine kinase activity but not the plasma membrane localization of the tsl S13 v-sea gene product. Erythroblasts transformed by tsl S13 can be induced to synchronously differentiate into erythrocytes in an erythropoietin (EPO)-dependent fashion. Analysis of erythrocyte-specific gene expression in tsl S13 erythroblasts reveals that the transformed, self-renewing erythroblasts obtained at permissive temperature already express all erythrocyte genes tested for, although at a low level. Upon differentiation induction, expression of erythrocyte-specific genes is not coordinately regulated but rather involves complex regulatory mechanisms that appear to be specific for the individual genes.

Mostly by cDNA cloning, well over 20 significantly related, GTP-binding proteins have been identified in mammalian cells. According to distinct structural features, these proteins, constituting the ras superfamily, can be separated into at least three families: ras, rho and ypt proteins (1). The genomic sequences of the H-, K-, N-and Rras genes only have been elucidated (2,3,4,5). Here we present the genomic sequence of the mouse yptl gene which