Multiple polymorphic α- and β-tubulin mRNAs are present in sea urchin eggs

Multiple α- and β-tubulin RNAs were found in the mature unfertilized eggs of the sea urchin Lytechinus pictus. The α-tubulin RNAs were polymorphic in number, size, and relative amounts in the eggs of different females. Five to seven different size classes [1.75-4.2 kilobases (kb)] were detected on RNA gel blots. All egg preparations contained variable amounts of 1.8- and 2.25-kb β-tubulin RNAs, and a few of them contained an additional 2.9-kb β-tubulin RNA. The total amount of α-tubulin RNA did not always parallel that of β-tubulin RNA. A portion of all of the various α- and β-tubulin RNAs were polyadenylylated. RNase H digestions ruled out the possibility that some of these RNAs represented a single transcript bearing different lengths of 3' poly(A). One class of α-tubulin RNAs (2.4-2.65 kb) was reduced to 2 kb by RNase H, suggesting the presence of internal oligo(A) regions. All of the egg β-tubulin RNAs sedimented as free ribonucleoprotein particles. Only a small portion of the 1.75- to 3.6-kb α-tubulin RNAs, but most of the 4.2-kb α-tubulin RNA, were found on polysomes before fertilization. In the 30-min embryo, small amounts of each of the various α- and β-tubulin RNAs were recruited onto polysomes. Thus, each of the multiple polymorphic α- and β-tubulin RNAs in the egg represent translationally competent mRNA.