The discovery of a protein, p63/6·9, that is synthesized by both somatic and germ cells and coded for by a gene, Tcp-1, within the t complex provides a molecular probe for examining transmission ratio distortion in t mice. Two electromorphs of this protein exist. The acidic protein (a) is encoded by t-haplotype chromosomes, while the basic protein (b) is encoded by wild-type 17th chromosomes. We have measured the relative amounts of p63/6·9a and p63/6·9b for various t-complex bearing males and for several stages of spermatogenesis. There was no correlation between the ratio of p63/6·9a to b and the magnitude of transmission ratio distortion but the relative amounts of these proteins present in testicular cells can vary depending on the method of labelling. In vivo labelling results in the detection of two-fold greater amounts of p63/6·9a while in vitro labelling produces equimolar amounts of these two proteins. These data suggest that unequal synthesis or degradation of the p63/6·9 proteins occurs during spermatogenesis. It is proposed that increased synthesis of p63/6·9a in vivo is an intrinsic property of t-haplotypes.

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