Regulation of Coronaviral Poly(A) Tail Length duringInfection

The positive-strand coronavirus genome of ~30 kilobase in length and subgenomic (sg) mRNAs of shorter lengths,are 5’ and 3’-co-terminal by virtue of a common 5’-capped leader and a common 3’-polyadenylated untranslatedregion. Here, by ligating head-to-tail viral RNAs from bovine coronavirus-infected cells and sequencing across theligated junctions, it was learned that at the time of peak viral RNA synthesis [6 hours postinfection (hpi)] the 3’ poly(A)tail on genomic and sgmRNAs is ~65 nucleotides (nt) in length. Surprisingly, this length was found to vary throughoutinfection from ~45 nt immediately after virus entry (at 0 to 4 hpi) to ~65 nt later on (at 6 h to 9 hpi) and from ~65 nt (at6 h to 9 hpi) to ~30 nt (at 120-144 hpi). With the same method, poly(U) sequences of the same lengths weresimultaneously found on the ligated viral negative-strand RNAs. Functional analyses of poly(A) tail length on specificviral RNA species, furthermore, revealed that translation, in vivo, of RNAs with the longer poly(A) tail was enhancedover those with the shorter poly(A). Although the mechanisms by which the tail lengths vary is unknown,experimental results together suggest that the length of the poly(A) and poly(U) tails is regulated. One potentialfunction of regulated poly(A) tail length might be that for the coronavirus genome a longer poly(A) favors translation.The regulation of coronavirus translation by poly(A) tail length resembles that during embryonal developmentsuggesting there may be mechanistic parallels