Coenzyme Q4 Homolog (COQ4)

The deduced 265-amino acid protein has an N-terminal mitochondrial localization sequence with a consensus cleavage site at pro22. COQ4 was predicted to be a soluble protein. Northern blot analysis detected a transcript of 1.3 to 1.4 kb in all tissues examined, with highest expression in liver, lung, and pancreas. EST database analysis and 5-prime RACE detected a splice variant that lacks exon 1 and initiates translation from an ATG codon within exon 2. The isoform encoded by this variant, COQ4 isoform-2, lacks the first 24 amino acids of full-length COQ4 isoform-1. Fluorescence-tagged COQ4 isoform-1 localized to mitochondria in transfected HeLa cells, whereas COQ4 isoform-2 localized mainly to the cytosol and to some extent the nucleus, but not to mitochondria.