Amplification in the leader sequence of late polyoma virus mRNAs.

Ribonuclease T1 fingerprints of the three "late" polyoma virus mRNAs show that oligonucleotides of the leader sequence are present in multiple copies in each mRNA. These oligonucleotides, however, appear unimolar in fingerprints of complete, continuous transcripts of the late strand of the viral DNA. Oligonucleotides which are represented only once in the DNA are thus reiterated in the mature mRNAs. Consequently, when mRNA was hybridized to the leader region of immobilized viral DNA, those copies present in excess of their genomic representation failed to hybridize and were released by RNAase treatment. Analysis of the RNAase-resistant hybrids revealed a series of leader species with complex sequence arrangements. We suggest that these complicated reiterated sequences are generated during the processing of a precursor RNA which extends several times around the genome. This RNA would be shortened by a series of splicing reactions which conserve sequences from the leader region and attach them to a suitable coding sequence.