Biochemical research on oogenesis: Oocytes of Xenopus laevis synthesize but do not accumulate 5S RNA of somatic type

The oocytes of amphibians and teleosts begin to accumulate 5S RNA several months before other components of the ribosomes become available. Two types of genes coding for 5S RNA are active during oogenesis of these animals. One type of genes is expressed only in oocytes. The other type is expressed in both oocytes and somatic cells. In this paper, we show that the oocytes of Xenopus laevis do not accumulate 5S RNA of somatic type. We conclude that the products of the two types of genes behave differently during oogenesis. One product is stored by the oocytes, whereas the other is not. The heterogeneity of 5S genes in Xenopus laevis might have arisen because oocytes and somatic cells needed different kinds of 5S RNA. These needs are met by molecules having different primary structures, different conformations, and different metabolic stabilities in vivo. We do not understand how these properties are related to one another.