SIMILAR EVOLUTIONARY PATTERNING AMONG REPEATED AND SINGLE-COPY NEMATODE MITOCHONDRIAL GENES

Ten of 12 mitochondrial protein-coding genes and the large (16S) mitoc hondrial rRNA gene have been identified and mapped within the Romanome rmis culicivorax mitochondrial genome. This transcriptional map differ s from other nematode mitochondrial DNAs (mtDNAs) with respect to gene order and transcriptional orientation of some genes. Several of these coding regions are components of a 3.0-kilobase mtDNA repeating unit, allowing a direct comparison of nucleotide and amino acid sequence co mposition for repeated and single copy genes. Analysis of protein-codi ng regions representing repeated (ND3, ND6) and single copy genes (ATP ase 6, cyt.b, COI, COIII, ND1, ND4, ND5), and four repeat-associated o pen reading frames (ORFs) with unassigned function have revealed strik ing similarities in nucleotide composition, amino acid frequencies, an d codon biases. Although we anticipated that reiterated protein coding regions might be evolving under relaxed selection, our results indica te that both repeated and unique mitochondrial genes appear subject to similar functional constraints.