Most sea urchin maternal mRNA sequences in every abundance class appear in both polyadenylated and nonpolyadenylated molecules

Abstract

The sequences in poly(A)-containing and -deficient RNA accumulated in sea urchin eggs were analyzed by hybridization to cDNA and single-copy genomic DNA. The reaction of poly(A) egg RNA to its homologous cDNA occurs over five orders of R 0 t. A standard computer fit to the reaction curves indicates three abundance classes with 32% of the poly(A) RNA in highly abundant sequences, 13% in moderately abundant sequences, and 55% in rare sequences. The calculated number of averaged-sized, 3000-nucleotide-long mRNA sequences in each of these classes was 2, 44, and 4600, respectively. Reactions of cDNA to total and poly(A)-deficient RNA indicate that less than half of the molecules containing any individual sequence carried a poly(A) segment large enough to bind to oligo(dT). A saturation hybridization to single-copy DNA complementary to egg RNA indicated that all rare class sequences are polyadenylated. About one-third are adenylated on 30 to 50% of their molecules; the remaining rare sequences are polyadenylated on about 5% of their molecules. Most sequences present in poly(A) RNA molecules in the egg are found associated with polysomes following fertilization. About 80 to 85% of the poly(A) maternal mRNA sequences in cDNA which reanneal to total sea urchin DNA react as-single-copy sequences, while 15 to 20% react as repetitive DNA sequences.