Spinach chloroplast mRNA for a 32 000 dalton polypeptide: size and localization on the physical map of the chloroplast DNA.

The RNA from chloroplasts of young spinach plants contains mRNAs which are translated in a cell-free protein synthesizing system from lysed rabbit reticulocytes. Using [35S]methionine to label the products of translation, the main peptides have apparent molecular weights of 55,000, 45,000, 40,000, 32,000, 20,000 and 17,000. The sizes of the mRNAs as estimated by sucrose gradient centrifugation under non-denaturing conditions are between 12 and 23 S. A prominent product synthesized with RNA isolated from young spinach plants has an approximate molecular weight of 32,000. The mRNA for this 32,000 dalton protein sediments at 14 S on sucrose gradient. The position of the DNA sequence coding for this mRNA on the restriction site map of spinach chloroplast DNA was determined by hybridization and hybrid-arrested translation. A preliminary transcription map shows that in RNA from spinach chloroplasts which is larger than 10 S different RNA species are present which hybridize to nearly all fragments of the larger of the two single-copy regions of the chloroplast DNA.