The nucleotide sequence adjacent to poly(A) in silk fibroin messenger RNA

The 3'-terminal nucleotide sequence of fibroin mRNA has been determined. A cDNA transcript primed by oligo(dT) hybridized to the poly(A) segment of fibroin mRNA was used to determine the sequence immediately adjacent to poly(A). A specific primer complementary to this sequence then allowed synthesis of 5'-terminally homogeneous transcripts amenable to analysis by rapid sequencing methods. The 3' terminus of fibroin mRNA contains an unusually long oligo(U) stretch, as well as the sequence A2UA3 recently found in 3' non-coding regions of other eukaryotic mRNAs. It lacks the oligonucleotides characteristic of the repetitive coding region of fibroin mRNA.