Unusual abundance of vertebrate 3-phosphate dehydrogenase pseudogenes.
ABSTRACT Only one gene coding for glyceraldehyde 3-phosphate dehydrogenase (GAPDH, EC 18.104.22.168), a key enzyme in the control of glycolysis, is known to be functional in man, mouse, rat and chicken. The gene has been localized to chromosome 12 in human and chromosome 6 in mouse. Only a single mRNA species has been found in chicken and rat. However, analysis of genomic DNA blots of various species with a cloned GAPDH cDNA probe has revealed large differences in the level of reiteration, ranging from one to over 200 copies. On this basis, we have grouped these organisms into three classes according to the number of GAPDH-related sequences they contain; one class with a unique representation (chicken), another class of relatively low reiteration (10-30 copies in man, hare, guinea-pig and hamster) and a third class of high reiteration (greater than 200 copies in mouse and rat). The third class represents the first reported occurrence of such an extreme number of pseudogenes related to an enzyme-coding gene and suggests that a dramatic amplification event took place between 15 and 25 million years ago.
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ABSTRACT: A single-stranded DNA-binding protein of Mr 35,000 (35K protein) was isolated from calf cerebral cortex by affinity chromatography on immobilized double-stranded and single-stranded DNA. Its localization in the nuclear compartment was demonstrated by im-munohistochemistry. Previous studies had uncovered a homologous nonhistone chromosomal protein in the nuclei of rat cerebral cortex neurons, cerebellar neurons, oligodendrocytes, and liver cells. The rat protein accumulated in the nuclear compartment of neurons in exact temporal coincidence with the arrest of cell division and the initiation of terminal differentiation. Therefore, in the present work, the 35K protein was tested for an activating role in RNA transcription. During the course of this study we became aware that the 35K protein was identical to a glycolytic enzyme, glyceraldehyde-3-phos-phate dehydrogenase (GAPDH, EC 22.214.171.124). When authentic GAPDH from rabbit skeletal muscle was injected into Xenopus laevis oocytes, it greatly stimulated RNA polymerase II transcription, whereas the 35K protein from caif brain did not. This apparent discrepancy was partially resolved by the finding that rabbit muscle GAPDH could be fractionated into two components by affinity chromatography on single-stranded DNA cellulose. Only 5% of the applied protein was retained on the column and could be eluted with a shallow salt gradient identical to the one used for the isolation of the 35K protein. This single-stranded DNA-binding component of rabbit muscle GAPDH did not stimulate transcription. Apparently, the 35K protein from calf brain corresponded to this single-stranded DNA-binding subfrac-tion, which explained its failure to activate transcription. So far, we have not been able to isolate the activating factor from calf brain but suggest that the temporal coincidence between the accumulation of GAPDH in rat neu-ronal nuclei during differentiation and the concomitant increase in transcriptional activity may not be fortuitous.Journal of Neurochemistry 07/2006; 47(1):54-62. DOI:10.1111/j.1471-4159.1986.tb02830.x · 4.24 Impact Factor