Late domain function identified in the vesicular stomatitis virus M protein by use of rhabdovirus-retrovirus chimeras

Little is known about the mechanisms used by enveloped viruses to separate themselves from the cell surface at the final step of budding. However, sma ll sequences in the Gag proteins of several retroviruses (L domains) have b een implicated in this process. A sequence has been identified in the M pro teins of rhabdoviruses that closely resembles the PPPPY motif in the L doma in of Rous sarcoma virus (RSV), an avian retrovirus. To evaluate whether th e PPPY sequence in vesicular stomatitis virus (VSV) M protein has an activi ty analogous to that of the retroviral sequence, M-Gag chimeras were charac terized. The N-terminal 74 amino acids of the VSV (Indiana) M protein, incl uding the PPPY motif, was able to replace the L domain of RSV Gag and allow the assembly and release of virus-like particles. Alanine substitutions in the VSV PPPY motif severely compromised the budding activity of this hybri d protein but not that of another chimera which also contained the RSV PPPP Y sequence. We conclude that this VSV sequence is functionally homologous t o the RSV L domain in promoting virus particle release, making this the fir st example of such an activity in a virus other than a retrovirus. Both the RSV and VSV motifs have been shown to interact in vitro with certain cellu lar proteins that contain a WW interaction module, suggesting that the L do mains are sites of interaction with unknown host machinery involved in viru s release.