Abstract
cDNA clones encoding two Photosystem I subunits of Chlamydomonas reinhardtii with apparent molecular masses of 18 and 11 kDa (thylakoid polypeptides 21 and 30; P21 and P30 respectively) were isolated using oligonucleotides, the sequences of which were deduced from the N-terminal amino acid sequences of the proteins. The cDNAs were sequenced and used to probe Southern and Northern blots. The Southern blot analysis indicates that both proteins are encoded by single-copy genes. The mRNA sizes of the two components are 1400 and 740 nucleotides, respectively. Comparison between the open reading frames of the cDNAs and the N-terminal amino acid sequences of the proteins indicates that the molecular masses of the mature proteins are 17.9 (P21) and 8.1 kDa (P30). Analysis of the deduced protein sequences predicts that both subunits are extrinsic membrane proteins with net positive charges. The amino acid sequences of the transit peptides suggest that P21 and P30 are routed towards the lumenal and stromal sides of the thylakoid membranes, respectively.
Highlights
In the photosynthetic electron transport chain, Photosystem I (PS I) catalyses the light-driven electron transfer from plastocyanin to ferredoxin.The absorption of a light quantum results in an electron transfer from the reaction-centre chlorophyll P700 to a series of electron acceptors, namely Ao, A 1 and the iron-sulphur centresThe nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession numbers X13495 and X13496.X, B and A
Abstract cDNA clones encoding two Photosystem I subunits of Chlamydomonas reinhardtii with apparent molecular masses of 18 and 11 kDa were isolated using oligonucleotides, the sequences of which were deduced from the N-terminal amino acid sequences of the proteins
Comparison between the open reading frames of the cDNAs and the N-terminal amino acid sequences of the proteins indicates that the molecular masses of the mature proteins are 17.9 (P21) and 8.1 kDa (P30)
Summary
In the photosynthetic electron transport chain, Photosystem I (PS I) catalyses the light-driven electron transfer from plastocyanin to ferredoxin. P700 is re-reduced by plastocyanin and the electron on the PSI acceptor side is transferred to ferredoxin. P700 and the first acceptors Ao, A~ and FeS x appear to be located on two chloroplast-encoded large subunits (80-85kDa). The PSI core complex contains several smaller subunits (
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