Cytochrome c Synthesis in Neurospora crassa

Citation

Scott, William Addison (1968) Cytochrome c Synthesis in Neurospora crassa. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JZZG-RZ19. https://resolver.caltech.edu/CaltechETD:etd-08042006-160643

Abstract

Part A: Cytochrome c synthesis was studied in the respiration deficient poky mutant of Neurospora crassa. Two cytochromes c, CI and CII, were detected. The two proteins were shown to differ by a secondary modification at residue 72. A precursor-product relationship was established; CII (lysine) is converted to CI (Lys-X). Lys-X was found to be a lysine derivative although the exact chemical nature of this residue is unknown. The kinetics of CI and CII synthesis in poky were compared to those of wild type and the respiration deficient mutants: mi-3, cyt-l, and po-f. In comparison to wild type, poky accumulates CII during the early stages of growth and has a delayed synthesis of CI. These events in the other mutants are normal even though they accumulate cytochrome c as does poky. Only CI was recovered from isolated poky mitochondria even though the whole cell contained both cytochromes c. In young poky over half of the cytochrome c is unbound. The conversion of CII to CI is thought to reflect a binding of cytochrome c to mitochondria since this event parallels the change of the poky phenotype to a more normal state. Part B: When wild type Neurospora is grown in high concentrations of chloramphenicol (4 mg./ml.), it exhibits a phenotype similar to that of the maternally inherited poky mutation. Both have no cytochromes a and b but have an excess of cytochrome c. Spontaneously occurring strains partially resistant to the drug were isolated. The resistance is controlled by more than one nuclear gene. The implications of these results are discussed in terms of the primary effect of the poky mutation and the differential inhibition of mitochondrial protein synthesis by chloramphenicol in cells of higher organisms.

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