[Study on the principles of base change in 4-fold degenerate sites of protein coding genes].

The relationship of transition and transversion of base change in 4-fold degenerate sites of coding genes of 6 proteins, which showed 70% homology in wmposition investigated. Taking into account of the effects of base composition on base substitution, it was found that the transition-transversion bias was evident but not as pronounced as in mitochondrial DNA. Comparison of different kinds of transition or transversion indicated that they happened with rather equal vate, with 0.65-0.73 for different kinds of transversion and 0.99 for A-G transition assuming that T-C transition was 1. The causes for transition-transversion bias is discussed and it is proposed that mutagens may play a role in it.