Purification and biochemical, cell biological analysis o a new human GTP-binding protein

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The human rab-2 gene codes a 24-kDa YPT1-related GTP-binding protein. In all the human cell lines examined, including hematopoietic, fibroblastic and tumor cells, three rab-2 transcripts of 3.5, 2.4 and 1.4 kb were detected. The 2.4- and 3.5-kb rab-2 RNA hybridized with the probe specific for the 3'-non-coding region of 2.4-kb transcript, but not the 1.4-kb RNA. These transcripts seemed to differ in the length of their 3'-non-translated regions due to terminations of the transcription and/or processing of the primary transcript at the alternative polyadenylation sites. The smaller 1.4-kb transcript was the most predominant in Molt-4 and U-937, while the 2.4-kb RNA was dominant in the other cell lines. The degradation rates of all the rab-2 transcripts wbre similarly as slow as beta-actin RNA, even in the two cell lines whose predominant species of the transcripts were different. Rab-2 protein was detected in the extracts of human cultured cells as one major band of 24 kDa and a more faint band of 25 kDa by both immunoblotting and immunoprecipitation. Only the 25-kDa protein was detected in HeLa and KOBK101 cells. In the COS-1 cells transfected with an expression vector carrying rab-2 cDNA, the rab-2 protein was mainly located in the cytoplasm.