Topography of the C. coli 5S RNA-protein complex as determined by crosslinking with dimethyl suberimidate and dimethyl-3,3'-dithiobispropionimidate.

5S RNA-protein complexes were prepared in vitro using partially purified E. coli 5S RNA and total E. coli 70S ribosomal proteins. The complexes were isolated from sucrose gradients and shown to contain proteins L5, L18, L25 and a fourth protein not heretofore characterized and designed L31. The complexes were treated with the crosslinking reagents dimethyl suberimidate and dimethyl-3,3'-dithiobispropionimidate. Both reagents gave identical patterns of crosslinked proteins when analyzed by one-dimensional polyacrylamide/dodecylsulfate gel electrophoresis. Dimers of L5-L31', L5-L18 and L18-L18 and a trimer containing L5, L18 and L31' were identified by diagonal polyacrylamide/dodecylsulfate gel electrophoresis of the proteins crosslinked with dimethyl-3,3'-dithiobispropionimidate. No crosslinking was detected between L25 and the other three proteins.