Leader sequences of coronavirus are altered during infection.

The life cycle of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) involves a unique process called discontinuous transcription by which a set of 3' coterminal subgenomic mRNAs (sgmRNA) with identical 5' leader sequences can be generated. The current study demonstrates that the replication intermediates of minus strand of subgenomic RNA (sgRNA) can be readily recovered from SARS-CoV infected cells. A novel sgmRNA (M-1) was identified as a short version of membrane (M) gene. Transcriptional regulatory sequences (TRS) of SARS-CoV and Mouse Hepatitis Virus (MHV) sgmRNAs contain a species specific core element (CE). The sizes of leader sequences in MHVs vary not only in different viral strains but also among different genes in the same strain. Leader alterations such as deletion and nucleotide substitution were observed in MHVs, while a dynamic one-orientation 'sequential deletion' was found among the leaders of 76 SARS-CoV isolates. These results imply that the leader sequence of coronavirus might be unstable and leader alterations during SARS-CoV transmission in humans might have negative impact on its viral infectivity.