Theoretical mechanisms for synthesis of carcinogen-induced embryonic proteins: XXIV. Repeated embryonic genes in liver.

Many embryonic genes may be sets of repeated genes. Processes of differentiation where the quantity of gene activity changes during embryogenesis may not reflect the transcription rate per se but instead be a result of the state of expression of constitutive repeated genes. Such repeated genes (in fact or theory) is dealt with here for embryonic, adult and neoplastic liver. Explanations are presented for 1) the variation in ATP: L-methionine S-adenosyltransferase activity in spontaneous hepatomas and embryonic liver; 2) differences tRNA L-methionine S-adenosyltransferase activity in spontaneous hepatomas and embryonic liver; 3) differences in tRNA methylase activity in embryonic liver, hepatomas of varying levels of differentiation, and ethionine treated liver; 4) relationships between rRNA genes and nucleolar organizers; and 5) the possibilities involving c-onc genes (proto-oncogenes) for situations of 'over-expression' in neoplastic and embryonic liver.