期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1998
卷号：95
期号：25
页码：14805-14810
DOI：10.1073/pnas.95.25.14805
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：{beta}1,4-Galactosyltransferase ({beta}4GalT-I) participates in both glycoconjugate biosynthesis (ubiquitous activity) and lactose biosynthesis (mammary gland-specific activity). In somatic tissues, transcription of the mammalian {beta}4GalT-I gene results in a 4.1-kb mRNA and a 3.9-kb mRNA as a consequence of initiation at two start sites separated by {approx}200 bp. In the mammary gland, coincident with the increased {beta}4GalT-I enzyme level ({approx}50-fold) required for lactose biosynthesis, there is a switch from the 4.1-kb start site to the preferential use of the 3.9-kb start site, which is governed by a stronger tissue-restricted promoter. The use of the 3.9-kb start site results in a {beta}4GalT-I transcript in which the 5'- untranslated region (UTR) has been truncated from {approx}175 nt to {approx}28 nt. The 5'-UTR of the 4.1-kb transcript [UTR(4.1)] is predicted to contain extensive secondary structure, a feature previously shown to reduce translational efficiency of an mRNA. In contrast, the 5'-UTR of the 3.9-kb mRNA [UTR(3.9)] lacks extensive secondary structure; thus, this transcript is predicted to be more efficiently translated relative to the 4.1-kb mRNA. To test this prediction, constructs were assembled in which the respective 5'-UTRs were fused to the luciferase-coding sequence and enzyme levels were determined after translation in vitro and in vivo. The luciferase mRNA containing the truncated UTR(3.9) was translated more efficiently both in vitro ({approx}14-fold) and in vivo (3- to 5-fold) relative to the luciferase mRNA containing the UTR(4.1). Consequently, in addition to control at the transcriptional level, {beta}4GalT-I enzyme levels are further augmented in the lactating mammary gland as a result of translational control.
关键词：5′-untranslated region/ in vitro translation/ in vivo translation/mammary gland/RNA secondary structure
