Molecular evolution of mammalian lactate dehydrogenase-A genes and pseudogenes: Association of a mouse processed pseudogene with a B1 repetitive sequence

Abstract

A mouse genomic clone containing a lactate dehydrogenase-A (LDH-A) processed pseudogene and a B1 repetitive element was isolated, and a nucleotide sequence of ~ 3 kb was determined. The pseudogene and B1 element are flanked by perfect 13-bp repeats, and the B1 sequence starts at 14 nucleotides 3' to the presumptive polyadenylation signal of the pseudogene. The nucleotide sequences of the LDH-A genes and processed pseudogenes from mouse, rat, and human were compared, and a phylogenetic tree was constructed. The rate and pattern of nucleotide substitutions in the LDH-A pseudogenes are similar to previously reported results (Li et al. 1984). The average rate of nucleotide substitutions in the LDH-A pseudogenes is 4.3 x 10-9/site/year. The substitutions of C → T and G → A are most frequent, and A → G substitutions are relatively high. The rate of synonymous substitutions in the LDH-A genes is 5.3 x 10-9, which is not significantly higher than the average rate of 4.7 x 10-9 for 35 mammalian genes. The rate of nonsynonymous substitutions in the LDH-A genes is 0.20 x 10-9, which is considerably lower than the average rate of 0.88 x 10-9 for 35 mammalian genes. Thus, the mammalian LDH-A gene appears to be highly conserved in evolution.