Characterization and expression of a cDNA, AmphiSDHD, encoding the amphioxus cytochrome b small subunit in mitochondrial succinate-ubiquinone oxidoreductase

Abstract

In this study, an amphioxus cDNA, AmphiSDHD, encoding the cytochrome b small subunit in mitochondrial succi–nate–ubiquinone oxidoreductase, was isolated from the gut cDNA library of amphioxus Branchiosioma belcheri tsingtauense. It is 1429 bp in length, with an open reading frame of 465 bp coding for a protein of 154 amino acids. The deduced protein contains a mitochondrial tar geting presequence of 65 amino acids rich in basic residues like arginine and hydroxy residues such as serine and threonine. Alignment of the amino acid sequences of AmphiSDHD and other eukaryotic SDHD proteins showed that AmphiSDHD has three transmembrane segments, and includes two histidine residues in the second transmembrane segment that are the putative binding sites for the heme b molecule. The phylogenetic tree constructed suggests that AmphiSDHD appears more closely related to vertebrate SDHD proteins than in–vertebrate ones. Northern blotting demonstrated that AmphiSDHD is ubiquitously expressed in amphioxus, being in line...