Properties of sea urchin embryo messenger RNA containing and lacking poly(A)

Various properties of nonhistone messenger RNA species containing poly(A), [+A]mRNA, and lacking poly(A), [−A]mRNA, are described: the rates of turnover of these mRNA classes are not significantly different, as indicated by their similar rates of entry into and decay from the cytoplasm; each mRNA class is essentially entirely transcribed from unique DNA sequences; the ratio of [+A] to [−A] nonhistone mRNA increases with increase in size of free polyribosome, although the average molecular weights of these mRNAs are similar in each polysomal size class. These results indicate that the [+A]mRNA species tend to be more fully loaded with ribosomes than the nonhistone [−A]mRNA species.