Nucleoids of pea chloroplasts: Characterization of proteins

Proteins from nucleoids of Pisum sativum L. chloroplasts were fractionated by extraction with increasing NaCl concentrations (0.1-2.0 M). Proteins wit h mol wts of 16, 20, and 22 kD were extracted by 0.4 M NaCl. Two proteins w ith mol wts of 18 and 40 kD were extracted by 2.0 M NaCl. In all probabilit y, these five proteins are associated with DNA by electrostatic interaction s. Using RP-HPLC, the composition of basic proteins from pea nucleoids was studied. Twenty-five fractions, including five major ones, were detected. S DS-PAGE showed that the predominant protein in fraction 12 was a 28-kD prot ein. The partial sequencing of this P28 protein and a subsequent search in the Swiss-Prot database showed that this protein was homologous to the ribo somal protein L19 of Saccharomyces cerevisiae. The putative functional role of basic proteins from nucleoids of chloroplasts is discussed.