Structure and expression of cytochrome f in an Oenothera plastome mutant.
The chloroplast mutant pm7 is one of a number of mutants derived from the plastome mutator (pm) line of Oenothera hookeri, strain Johansen. Immunoblotting showed that this mutant accumulates a protein that is cross-antigenic with cytochrome f, but five kilodaltons larger than the mature wild-type protein. Since cytochrome f is known to be translated on plastid ribosomes as a precursor with an amino-terminal extension, it is proposed that the unprocessed cytochrome f precursor accumulates in pm7. In addition to this precursor-sized cytochrome f protein, some mature-sized cytochrome f was also found in the mutant plastids. The pm7 mutation is inherited in a non-Mendelian fashion; but no alterations in chloroplast DNA restriction patterns, or differences in DNA sequence in the region encoding cytochrome f, were found in a comparison of the wild-type and pm7 chloroplast DNAs. Although the mutant was capable of synthesizing heme, no covalently-bound heme, normally found associated with mature, functional, cytochrome f was detected in the mutant at sizes expected for the presumed precursor, or for mature cytochrome f. These results indicate that the aberrant accumulation of a precursor-sized cytochrome f in pm7 is not due to a lesion directly in the plastid gene encoding cytochrome f, petA, or to a deficiency in the ability of the mutant plastids to synthesize or accumulate heme.
Johnson
E M
EM
Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824.
Sears
B B
BB
D001483:Base Sequence; D002736:Chloroplasts / Q000032:analysis / Q000378:metabolism*; D003580:Cytochromes / Q000235:genetics*; D045348:Cytochromes f; D004591:Electrophoresis, Polyacrylamide Gel; D017343:Genes, Plant; D006418:Heme / Q000032:analysis; D007106:Immune Sera; D008969:Molecular Sequence Data; D009154:Mutation; D010944:Plants / Q000235:genetics*; D015183:Restriction Mapping
D003580:Cytochromes; D007106:Immune Sera; D006418:Heme; D045348:Cytochromes f