Selection of a cDNA clone for chicken high-mobility-group 1 (HMG1) proteinthrough its unusually conserved 3 '-untranslated region, and improved expression of recombinant HMG1 in Escherichia coli

Screening of cDNA libraries for the homologous vertebrate proteins high mob ility group (HMG) 1 and 2 using DNA probes based on the coding sequences is likely to result in isolation of both HMG1 and HMG2 clones, as well as pse udogenes, which may be transcribed at low levels. However, the 3'-untransla ted regions (UTRs) of HMG1 and 2 are quite distinct, and unusually conserve d across species. We have used this property to select the true chicken HMG 1 cDNA clone from a chicken lymphocyte cDNA library in lambda gt11, using a probe based on the 3'-UTR of rat HMG1 cDNA. The chicken HMG1 cDNA clone is very similar to all the complete HMG1 cDNA clones isolated so far. We sugg est that the sequence designated chicken HMG1 in the GenBank Data Library ( Accession number D14314) is, in fact, that of HMG2a [and moreover that the recently reported mouse clone (Accession number AF022465), proposed to enco de a new HMG protein, HMG4, is also likely to encode an HMG2a, based on the translated amino-acid sequence and 3'-UTR]. We also report much improved e xpression of intact recombinant HMG1 in Escherichia coli by the use of chlo ramphenicol rather than ampicillin selection and conditions that limit cell growth. This should be general for all members of the HMG1 land 2) family which may be toxic to cells (possibly because of the long acidic tail), and may also prove useful in the production of other such proteins. (C) 1998 E lsevier Science B.V. All rights reserved.