Biochemical research on oogenesis: Oocytes and liver cells of the teleost fish Tinca tinca contain different kinds of 5S RNA

Previtellogenic oocytes of Tinca tinca accumulate very large amounts of 5S RNA. We show here that 5S RNA stored in oocytes differs from liver 5S RNA in 3 out of 120 nucleotides. Liver and oocyte 5S RNAs, therefore, are produced by different genes. Both kinds of 5S genes are active in oocytes. However, only 5S RNA of the oocyte type accumulates in these cells. In Tinca tinca as in Xenopus laevis, oocyte-type and somatic-type 5S RNAs differ by three properties, ie., primary structure, conformation, and metabolic stability. Nucleotide substitutions occur in different positions in oocyte and somatic 5S RNAs of Tinca tinca and Xenopus laevis. We do not understand how different sets of nucleotide substitutions confer to 5S RNAs of both species similar properties in vivo, namely, increased metabolic stability.