Significance of the YLDL motif in the M protein and Alix/AIP1 for Sendai virus budding in the context of virus infection

Sendai virus (SeV) M protein has a YLDL motif, which is essential for budding of virus-like particles (VLPs) by expression of the M protein. We investigated the importance of the YLDL motif for SeV budding. Virus budding of an M-deficient SeV was not rescued by transient expression of motif mutants, M-A2 (ALDA) and M-A4 (AAAA), and viruses possessing those mutations hardly propagated in cultured cells. However, a budding-competent revertant virus, SeV M-A2R, was obtained from SeV M-A2, and nucleotide sequencing showed an ALDV sequence at the motif instead of the ALDA sequence derived from M-A2. The M-A2R protein rescued budding of an M-deficient SeV, formed VLPs when expressed with viral C protein, and restored the capacity to bind with Alix/AIP1. The results indicate that the YLDL motif is essential for efficient budding in the context of virus infection and suggest involvement of Alix/AIP1 in SeV budding.