| Abstract: | We have cloned a complementary DNA for pre-apocytochrome c-552 from Chlamydomonas reinhardtii. The deduced sequence of the mature protein shows high homology to those of cytochromes c-553 from cyanobacteria. Its homology to mitochondrial cytochrome c or bacterial photosynthetic cytochrome c2 is lower and appears to be concentrated in sequences around amino acids involved in the interaction with heme. With respect to primary sequence, the "transit sequence" for cytochrome c-552 appears to show no homology to other transit sequences for nuclear encoded chloroplast proteins. However, based on analogy to transit sequences for other proteins (Daldal, F., Cheng, S., Applebaum, J., Davidson, E., and Prince, R. C. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 2012-2016; Goldschmidt-Clermont, M., and Rahire, M. (1986) J. Mol. Biol. 191, 421-432; Smeekens, S., de Groot, M., van Binsbergen, J., and Weisbeek, P. (1986) Cell 46, 365-375) the transit sequence of cytochrome c-552 can be divided into envelope-traversing and thylakoid-traversing domains. Cytochrome c-552 appears to encoded by a single nuclear gene in C. reinhardtii. The gene is expressed exclusively in Cu(II)-deficient cells. |
