lightstrand

Lightstrand, or the light strand (L-strand), is the designation for one of the two strands of vertebrate mitochondrial DNA. It is named for its relatively lighter buoyant density and lower guanine content compared with the heavy strand (H-strand). The two strands are complementary and form a double helix; they are transcribed in opposite directions, producing distinct RNA transcripts.

In most vertebrates, the heavy strand carries the majority of protein-coding genes, while the light strand encodes a smaller subset. Notably, the ND6 protein-coding gene and several transfer RNA genes are located on the L-strand. The transcription of the L-strand yields RNA transcripts that contribute to mitochondrial gene expression and are processed in coordination with the H-strand transcripts.

Like the heavy strand, the light strand participates in the replication and maintenance of the mitochondrial genome. The arrangement of genes on the two strands is highly conserved within lineages and reflects the compact, overlap-rich organization characteristic of mitochondrial DNA. The L-strand’s gene content and transcriptional orientation help regulate overall mitochondrial function and expression.

Mutations in L-strand genes can affect mitochondrial function and are studied in evolutionary biology, forensic genetics, and clinical research on mitochondrial diseases. Analyses of L-strand sequences, in combination with the heavy strand, support investigations into species relationships, maternal ancestry, and the molecular basis of mitochondrial disorders.