Appearance of RNA with a specific size class of poly(A) in oocytes and eggs in HCG-stimulated Xenopus laevis females.

Using a 3H-poly(U) binding technique, poly(A) content has been measured in Xenopus laevis eggs consisting of two groups: one was obtained from females 12 to 16 hr after a single injection of human chorionic gonadotropin (HCG) (designated "unstimulated" eggs), and the other was obtained one week later from the same females by the second injection of the hormone ("stimulated" eggs). The stimulated egg contained about a 1.2-fold larger amount of poly(A) than the unstimulated one. Gel electrophoresis has revealed that this slight but reproducible increase in the poly(A) content was due to the production of a specific size class of poly(A) (i.e., about 80 nucleotides long). This poly(A) was also detectable in the oocytes obtained one week after a single injection but not in those from uninjected females. Poly(A)+RNA was analyzed by sucrose density gradient centrifugation, and it has been shown that most of the 80 nucleotide-long poly(A) sequences in the stimulated eggs were associated with RNA whose size distribution was less heterogeneous than, and hence distinguishable from, that of the bulk poly(A)+RNA. The possibility is discussed that HCG hormone may stimulate the synthesis of a specific class of poly(A)+RNA in smaller oocytes, which may not normally take place to a significant extent during maturation.