ABSTRACT
Ran genes encode a family of well-conserve small nuclear GTPases (Ras-related nuclear proteins), whose function is implicated in both normal cell cycle progression and the transport of RNA and proteins between the nucleus and the cytoplasm. Previous studies of Ran proteins have utilized cell-free systems, yeasts, and cultured mammalian cells. We have now characterized patterns of Ran gene expression in the mouse. Serum starvation suppressed Ran gene transcription in mouse 3T3 cells. Ran mRNA reappeared in cells within 3 h after refeeding. A single Ran mRNA species was detected at low levels in most somatic tissues of the adult mouse. In testis, this Ran mRNA was abundant, as were other larger transcripts. Analysis of testis-derived Ran cDNA clones revealed the presence of two transcripts, one specifying an amino acid sequence identical to that of human Ran/TC4 and one specifying an amino acid sequence 94% identical. Northern blotting and reverse transcriptase-PCR assays with oligonucleotide probes and primers specific for each transcript demonstrated that the isoform identical to Ran/TC4 was expressed in both somatic tissues and testis, while the variant form was transcribed only in testis. The existence of tissue-specific Ran isoforms may help to rationalize the diverse roles suggested for Ran by previous biochemical studies.
Subject(s)
GTP Phosphohydrolases/metabolism , Nuclear Proteins/metabolism , 3T3 Cells , Amino Acid Sequence , Animals , Base Sequence , DNA, Complementary/genetics , Female , GTP Phosphohydrolases/genetics , Gene Expression , Humans , Male , Mice , Molecular Sequence Data , Nuclear Proteins/genetics , Phylogeny , Polymerase Chain Reaction , RNA, Messenger/genetics , RNA, Messenger/metabolism , Sequence Homology, Amino Acid , Testis/metabolism , Tissue Distribution , ran GTP-Binding ProteinABSTRACT
Over 50 proteins related to the mammalian H-, K-, and N-RAS GTP binding and hydrolyzing proteins are known. These relatively low molecular weight proteins are usually grouped into four subfamilies, termed true RAS, RAS-like, RHO, and RAB/YPT, based on the presence of shared amino acid sequence motifs in addition to those involved in guanine nucleotide binding. Here, we apply parsimony analysis to the overall amino acid sequences of these proteins to infer possible phylogenetic relationships among them.
Subject(s)
Biological Evolution , Genes, ras , Multigene Family , Proto-Oncogene Proteins p21(ras)/genetics , Amino Acid Sequence , Animals , HumansABSTRACT
The Polymerase Chain Reaction was used to amplify ras and ras-like sequences from two human cDNA libraries. Members corresponding to each of the three major ras-subfamilies (ras, rho, and rab/YPT) were identified. The one homologous to rab/YPT, referred to here as YL8, appears to be the human homolog of the recently reported Schizosaccharomyces pombe YPT3 gene. The YL8 gene could encode a guanine nucleotide binding protein of 216 amino acids with about 70% amino acid sequence identity to S. pombe YPT3, and is transcriptionally active in a variety of human cell lines.
Subject(s)
Genes, ras , Schizosaccharomyces/genetics , Amino Acid Sequence , Base Sequence , Blotting, Northern , Blotting, Southern , DNA/analysis , Humans , Molecular Sequence Data , Polymerase Chain Reaction , RNA/analysis , Saccharomyces cerevisiae/genetics , Sequence Homology, Nucleic AcidABSTRACT
A mixed-oligonucleotide probe was used to identify four ras-like coding sequences in a human teratocarcinoma cDNA library. Two of these sequences resembled the rho genes, one was closely related to H-, K-, and N-ras, and one shared only the four sequence domains that define the ras gene superfamily. Homologs of the four genes were found in genomic DNA from a variety of mammals and from chicken. The genes were transcriptionally active in a range of human cell types.
