GENOMICS 49, 247–252 (1998) ARTICLE NO. GE985214 Hmg4, a New Member of the Hmg1/2 Gene Family T. Vaccari,* M. Beltrame,* S. Ferrari,* ,1 and M. E. Bianchi * , ² ,2 * Dipartimento di Genetica e di Biologia dei Microrganismi, via Celoria 26, 20133 Milan, Italy; and ² DIBIT, San Raffaele Scientific Institute, via Olgettina 58, 20132 Milan, Italy Received October 17, 1997; accepted January 12, 1998 scription factors, bind to DNA through the minor High mobility group (HMG) proteins are abundant groove, and bend the DNA segment to which they are components of mammalian nuclei and fall into three bound. Thus, both HMGI(Y) and HMG1/2 are consid- families. The members of one such family, HMG1 and ered ‘‘architectural’’ factors, necessary for the correct HMG2, are ubiquitously expressed and facilitate the geometrical assembly of multiprotein complexes on formation of nucleoprotein complexes where the DNA DNA (Tjian and Maniatis, 1994). is sharply bent. We have identified a mouse cDNA that HMG1 is a very abundant and highly conserved non- codes for a novel 200-amino-acid protein of the histone protein that is present in all vertebrate nuclei. HMG1/2 family, which we called HMG4. The mouse HMG1-like proteins probably exist in all eukaryotic Hmg4 gene is highly expressed in the embryo; Hmg4 cells (reviewed by Bianchi, 1995; Bustin and Reeves, transcripts are barely detectable in adult tissues. The 1996). The closely related mammalian protein HMG2 human HMG4 gene, which is extremely similar to its is also ubiquitously expressed and, to our knowledge, mouse homolog, has been sequenced as part of chro- has completely overlapping functions with HMG1. In mosome X, band q28. HMG4, HMG1, and HMG2 pro- vitro mammalian HMG1 and HMG2 bind with high teins have been highly conserved during vertebrate affinity to DNA containing sharp bends or kinks (Bian- evolution, suggesting that each has at least some chi et al., 1989; Pil and Lippard, 1992; L. Ronfani and unique property. It is possible that HMG4 is required M. E. Bianchi, unpublished) and have the ability to during development.  1998 Academic Press introduce transient bends or kinks into linear DNA molecules (Paull et al., 1993; Pil et al., 1993). HMG1 has long been considered a structural component of INTRODUCTION chromatin (van Holde, 1988), but we recently showed that it is not a component of condensed metaphase High mobility group (HMG) proteins are a diverse chromosomes, and it is loosely associated to chromatin group of nuclear proteins, first identified because of during interphase (Falciola et al., 1997). Rather, HMG1 their physical abundance and small molecular weight and 2 establish protein – protein contacts with TFIIA – (for reviews, see Bianchi, 1995; Bustin and Reeves, TFIID, several HOX and OCT proteins, and the proges- 1996). They fall into three families: terone nuclear receptor; they facilitate the binding of (1) the HMGI(Y) family, composed of HMGI and these transcription factors to target sites on DNA and HMGY, which derive from the same transcript through transcriptional activation (On ˜ ate et al., 1994; Shykind alternative splicing, and closely related proteins, like et al., 1995; Zappavigna et al., 1996; Zwilling et al., HMGI-C; 1995). In fact, the facilitating role of HMG proteins (2) HMG14 and HMG17, which associate with the in nucleoprotein formation may extend to other DNA core histones within nucleosomes; and transactions; HMG1/2 are probably involved in V(D)J (3) HMG1 and HMG2. recombination (Agrawal and Schatz, 1997; van Gent et al., 1997). Although the three families are completely dissimilar We report here that another member of the with regard to primary sequence and 3-D structure, HMG1/2 family exists. This novel protein, which we HMGI(Y) and HMG1/2 both interact with several tran- called HMG4 (high mobility group 4) has the same do- main structure of the known HMG1/2 proteins; like- Sequence data from this article have been deposited with the Gen- wise, mouse and human HMG4 genes are organized in Bank Data Library under Accession No. AF022465. 1 Current address: EMBL, Meyerhofstrasse 1, D-69117 Heidelberg, a manner similar to that of the HMG1 and HMG2 Germany. genes. It is clear that HMG4, HMG1, and HMG2 pro- 2 To whom correspondence should be addressed at Dipartimento teins diverged before the mammalian – bird separation di Genetica e di Biologia dei Microrganismi, via Celoria 26, 20133 and were all very conserved since, suggesting that each Milano, Italy. Telephone: /39-2-26605238. Fax: /39-2-2664551. E-mail: bianchm@dibit.hsr.it. has at least some unique property. HMG4 may be re- 247 0888-7543/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.