The histidines of the bacterial ribosome: a tritium exchange study.

The accessibility of histidines in the E. coli 30S subunits was assessed by exchange of C-2 histidine protons with tritiated water at 37 degrees C. The absence of exchange at acidic pH allowed the separation and identification of individual proteins without loss of histidine labelling. Only the two ribosomal proteins S5 and S6 exhibited significant exchange. No gross change of accessibility was detected in the 70S ribosome couples.