A leader sequence is present on mRNA A of avian infectious bronchitis virus.

The subgenomic mRNAs of the fowl coronavirus infectious bronchitis virus (IBV) form a 3' co-terminal or 'nested' set. The RNase T1 oligonucleotide mapping data which demonstrated this form of sequence organization provided no evidence for the presence of non-contiguous (leader) sequences fused to the 5' termini of the mRNAs. However, we have been able to demonstrate, by extension of an end-labelled synthetic oligonucleotide primer, the presence of a leader sequence on IBV mRNA A. Sequencing by the chemical degradation method of the extended product has yielded the almost complete sequence of the 60 base leader and its point of fusion to the sequence of the virus genomic RNA.