Reference "The PSI-K subunit of photosystem I from barley (Hordeum vulgare L.). Evidence for a gene duplication of an ancestral PSI-G/K gene"

Reference ID

8731

Title

The PSI-K subunit of photosystem I from barley (Hordeum vulgare L.). Evidence for a gene duplication of an ancestral PSI-G/K gene

Source

The Journal of biological chemistry, 1993, vol. 268, pp. 18912-18916

Authors (5)

Kjaerulff-S	Andersen-B
Nielsen-V-S	Moller-B-L
Okkels-J-S

Abstract

Photosystem I of barley contains a polypeptide with an apparent molecular mass
of 7 kDa when isolated using the detergent n-decyl-beta-D-maltopyranoside. The
7-kDa polypeptide is lost from the PS I complex isolated using Triton X-100. The
7-kDa polypeptide and a corresponding full-length cDNA clone have been isolated.
Based on high sequence similarity to an N-terminal sequence of PSI-K from
spinach and to the deduced amino acid sequence of Psak from Chlamydomonas
reinhardtii the 7-kDa barley polypeptide is identified as PSI-K. The cDNA clone
encodes a precursor polypeptide of 131 amino acid residues with a calculated
molecular mass of 13,726 Da. The transit peptide shows characteristics of
polypeptides imported into the chloroplast. PSI-K has two hydrophobic regions
predicted to be membrane-spanning alpha-helices. In vitro expressed prePSI-K
polypeptide was imported into intact chloroplasts, whereas an in vitro expressed
prePSI-K lacking 7 amino acid residues (Met-Ala-Ser-Gln-Leu-Ser-Ala) at the N-
terminal end of the transit peptide failed to be imported. The mRNA encoding PSI-
K increases during illumination. PsaK is located in a single locus in the
genome. PSI-K has significant similarity to PSI-G. When comparing the barley PSI-
K and PSI-G with the reported PSI-K sequence from Synechococcus vulcanus, the
degree of similarity is equal, suggesting that an ancestral gene has been
duplicated in a chloroplast progenitor but not in a cyanobacterial.