Evolution of a homopurine-homopyrimidine pentanucleotide repeat sequence upstream of the human inducible nitric oxide synthase gene

Gene. 1997 Dec 19;204(1-2):165-70. doi: 10.1016/s0378-1119(97)00538-6.


We have identified a highly polymorphic pentanucleotide repeat (CCTTT)n within the 5'-putative promoter region of the human inducible nitric oxide synthase gene (iNOS, NOS2). Using a pair of specific primers derived from the human iNOS gene, we have also amplified this iNOS repeat in DNA from the following species: chimpanzee, gorilla, orangutan and macaque. As is found in man, both chimpanzees and gorillas are polymorphic at this locus. In contrast, the locus is monomorphic in macaques and orangutans. While the average number of repeats is similar in gorilla and man, there are considerably fewer repeats in chimpanzees. A comparison of the sequences flanking the (CCTTT)n repeats among these closely related species demonstrates the presence of long stretches of homopurine-homopyrimidine residues. Similar polypurine/polypyrimidine stretches have been identified in the promoter regions of a number of other vertebrate genes where they have been associated with transcriptional regulation, although a role for the (CCTTT)n repeat array in the human iNOS gene has not yet been demonstrated.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • DNA, Complementary
  • Evolution, Molecular*
  • Gorilla gorilla
  • Humans
  • Macaca
  • Microsatellite Repeats*
  • Molecular Sequence Data
  • Nitric Oxide Synthase / genetics*
  • Nitric Oxide Synthase Type II
  • Pan troglodytes
  • Pongo pygmaeus
  • Purines
  • Pyrimidines
  • Sequence Homology, Nucleic Acid


  • DNA, Complementary
  • Purines
  • Pyrimidines
  • NOS2 protein, human
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type II

Associated data

  • GENBANK/X97821