Beta1,4-galactosyltransferase and lactose biosynthesis: recruitment of a housekeeping gene from the nonmammalian vertebrate gene pool for a mammary gland specific function

J Mammary Gland Biol Neoplasia. 1998 Jul;3(3):315-24. doi: 10.1023/a:1018719612087.


Beta1,4-galactosyltransferase (beta4GalT-I) is a constitutively expressed trans-Golgi enzyme, widely distributed in vertebrates, which synthesizes the beta4-N-acetyllactosamine structure commonly found in glycoconjugates. In mammals beta4GalT-I has been recruited for a second biosynthetic function, the production of lactose; this function takes place exclusively in the lactating mammary gland. In preparation for lactose biosynthesis, beta4GalT-I enzyme levels are increased significantly. We show that mammals have evolved a two-step mechanism to achieve this increase. In step one there is a switch to the use of a second transcriptional start site, regulated by a stronger, mammary gland-restricted promoter. The transcript produced is distinguished from its housekeeping counterpart by the absence of approximately 180 nt of 5'-untranslated sequence. In step two, this truncated transcript is translated more efficiently, relative to the major transcript expressed in all other somatic tissues.

Publication types

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

MeSH terms

  • Animals
  • Female
  • Gene Pool*
  • Humans
  • Lactose / biosynthesis*
  • Lactose Synthase / genetics*
  • Lactose Synthase / metabolism*
  • Mammals
  • Mammary Glands, Animal / enzymology*
  • Promoter Regions, Genetic
  • Vertebrates / genetics*


  • Lactose Synthase
  • Lactose