Full length cDNAs encoding the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rat and man have been isolated and sequenced. Many GAPDH gene-related sequences have been found in both genomes based on genomic blot hybridization analysis. Only one functional gene product is known. Results from genomic library screenings suggest that there are 300-400 copies of these sequences in the rat genome and approximately 100 in the human genome. Some of these related sequences have been shown to be processed pseudogenes. We have isolated several rat cDNA clones corresponding to these pseudogenes indicating that some pseudogenes are transcribed. Rat and human cDNAs are 89% homologous in the coding region, and 76% homologous in the first 100 base pairs of the 3'-noncoding region. Comparison of these two cDNA sequences with those of the chicken, Drosophila and yeast genes allows the analysis of the evolution of the GAPDH genes in detail.

The DNA binding activities of some basic region and putative helix-loop-helix (bHLH) -

No abstract

The helix-loop-helix transcription factor E2A plays important roles not only in promoting cellular differentiation but also in suppressing cell growth. Id proteins, the inhibitors of E2A, have opposite effects on cell differentiation and growth. To understand the mechanisms by which E2A suppresses cell growth, we examined the role of E2A in regulating the expression of the cyclin-dependent kinase inhibitor p21 CIP1/WAF1/SDI1 , which prevents cell cycle progression upon overexpression. By using transient-cotransfection assays of luciferase reporter constructs in HeLa cells, we have found that overexpression of E2A can transcriptionally activate the p21 gene. To identify the sequences that mediate this activation in the promoter of the p21 gene, we carried out mutational analyses. Out of the eight putative E2A-binding sequences (E1 to E8) in the promoter, the E1 to E3 sequences located close to the transcription start site are found to be essential. In addition, loss of the E boxes in the promoter also reduces p21 expression without cotransfection with E2A in HIT pancreatic cells, where the endogenous E2A-like activity is high. Furthermore, we have also shown that overexpression of E2A in 293T cells activates expression of the endogenous p21 gene at both the levels of mRNA and protein. In correlation with the finding that E47 overexpression leads to growth arrest in NIH 3T3 cells, we have shown that Id1 overexpression in NIH 3T3 cells accelerates cell growth and inhibits p21 expression. Taken together, these results provide insight into the mechanisms by which E2A and Id proteins control cell growth.