Identification of an Escherichia coli S1-like protein in the spinach chloroplast ribosome

Abstract

Antibodies directed against E. coli ribosomal protein S1 were used in immunoblotting assays to search for an S1-like protein in the ribosome of spinach chloroplast. An immunological cross-reaction was reproducibly detected on the blots and inhibition experiments have demonstrated its specificity. The chloroplastic ribosomal protein which has epitopes common to antigenic determinants of the E. coli protein S1 was identified as being protein S2/S3.

Chloroplast ribosomes and protein synthesis.

“…A nuclear gene encoding this protein has been identified in spinach (178,179) and shown to have a light-independent, leaf-specific pattern of expression under the control of a negative nuclear factor, SlF, that down-regulates its promoter (740). Hahn et al (240) reported that monoclonal antisera to E. coli Si reacted with a chloroplast protein of spinach. Polyclonal antisera to two chloroplast-synthesized ribosomal proteins of C. reinhardtii ("S-7" and "S-11" [547]) reacted with E. coli Si (510), as did antisera to mixed chloroplast ribosomal proteins of spinach (119).…”