A shifty stop for a hairy tail

Olia, Adam S.; Cingolani, Gino

The tail apparatus of the bacteriophage SPP1 is an extraordinary ~1600-Ã…-long molecular machine. The tail mediates attachment of the virus to the host surface receptor, as well-as ejection of the viral genome into the host. The distal tip of the tail binds the extracellular ectodomain of the Bacillus subtilis receptor YueB, while the tail tube provides a conduit to funnel the viral genome into the host. This process, which culminates with the ejection of the ~44 kb of viral DNA across the thick, cell envelope of the Gram-positive bacterial cell, takes place in a time scale of seconds to minutes and represents a remarkable example of biotransformation. In this issue of Molecular Microbiology, Auzat et al. provide compelling evidence that the two major structural proteins of the SPP1 tail, gp17.1 (~19.1 kDa) and gp17.1* (~28 kDa), share a common N-terminal sequence, and that gp17.1* is generated by a translational frameshift in the gene 17.1. The extra domain fused to gp17.1* is synthesized by a +1 programmed translational frame-shift at the end of gene 17.1, which leads to the synthesis of approximately one gp17.1* for every three equivalents of gp17.1. This finding extends our current knowledge of translational frameshifts and provides a framework to understand how Siphoviridae phages like SPP1 have developed long-tail machines using only two major structural proteins.