Required for dimerization of active 70S ribosomes into 100S ribosomes; when added to monomeric 70S ribosomes stimulates formation of 100S dimeric ribosomes. Unlike E.coli, 100S ribosomes are present during exponential growth, peak during early stationary phase and then decrease (shown for strain NBRC 3060). Interacts with 100S ribosomes during exponential growth, as 100S ribosomes decrease (after 7 hours) also found associated with 70S ribosomes. Expressed by 2 hours growth, increases to maximal concentration by 7 hours and remains high (stationary phase) (at protein level). More protein is found in cells growing under nutrient-deficient conditions. Belongs to the HPF/YfiA ribosome-associated protein family. Long HPF subfamily.