When cells are starved, they tend to cannibalize excess proteins. Kuroda et al. (see the Perspective by Gottesman and Maurizi) examined this process in bacteria and discovered that inorganic polyphosphate appears to be a key factor in promoting the specific degradation of unassembled (excess) ribosomal subunits, presumably in order to recycle their constituent amino acids. They propose that the inorganic polyphosphate binds noncovalently to the ribosomal proteins and targets them for degradation by the adenosine triphosphate-dependent protease, Lon.
A. Kuroda, K. Nomura, R. Ohtomo, J. Kato, T. Ikeda, N. Takiguchi, H. Ohtake, A. Kornberg, Role of inorganic polyphosphate in promoting ribosomal protein degradation by the Lon protease in E. coli. Science 293, 705-708 (2001). [Abstract] [Full Text]
S. Gottesman, M. R. Maurizi, Surviving starvation. Science 293, 614-615 (2001). [Full Text]