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

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