Abstract
Total RNA, extracted from mature oocytes and tadpoles of
Xenopus laevis, was used as a template for
in vitro protein synthesis. The oocyte RNA is markedly deficient in abundant mRNA species by comparison to tadpole RNA or other somatic RNAs, in agreement with previous experiments using RNA-cDNA hybridization analysis (
S. Perlman and M. Rosbash, 1978,
Develop. Biol.
63, 197–212
). Oocyte pA
+ RNA is also larger than tadpole pA
+ RNA or other somatic pA
+ populations. The larger oocyte pA
+ RNA and smaller oocyte pA
+ RNA are equally good templates for
in vitro protein synthesis, which implies that much, and perhaps all, of the large oocyte pA
+ RNA is bona fide mRNA. We suggest that the relatively large size of the oocyte pA
+ RNA population is due, at least in part, to the relative lack of abundant mRNA species in the population. This suggestion follows from the observation of
0. Meyuhas and R. P. Perry (1979,
Cell
16, 139–148
) that L-cell-abundant mRNAs are preferentially small and rare mRNAs preferentially large. Most of the oocyte pA
+ sequences are also present in tadpoles and are still adenylated at this stage. Oocyte proteins synthesized
in vivo do not appear deficient in abundant proteins, suggesting that a translational control mechanism operates to select certain pA
+ RNAs at higher frequencies than others.