on SHORT COMMUNICATION Cloning and Mapping of the XRN2 Gene to Human

SHORT COMMUNICATIONCloning and Mapping of the XRN2Gene to HumanChromosome20p11.1–p11.2Min Zhang,Long Yu,1Yurong Xin,Peirong Hu,Qiang Fu,Cong Yu,and Shouyuan Zhao The Institute of Genetics,Fudan University,Shanghai200433,People’s Republic of ChinaReceived February12,1999;accepted April21,1999The Dhm1gene is the mouse homologue of the dhp1؉gene of Schizosaccharomyces pombe,which is involved in homologous recombination and RNA me-tabolism,such as RNA synthesis and RNA traffick-ing,in plementation analysis showed the Dhm1gene on a multicopy plasmid can rescue the temperature-sensitivity mutation of dhp1ts and the lethality of the dhp1null mutation.Thisfinding suggests that Dhm1has a function in mouse similar to that of dhp1؉.The human homologue of this gene, XRN2,has been identified.A 3.6-kb transcript of XRN2was detected in16tissues examined and was more abundant in testis.By radiation hybrid panel mapping,the XRN2gene was localized to chromo-some20p11.1–p11.2between markers D20S180and D20S871.©1999Academic PressHomologous recombination is a universal cellular process involved in both prokaryotes and eukaryotes. It is not only the major process for generating genetic diversity but also an important process involved in DNA repair.Though there are differences among them,several homologous recombination models have all regarded the DNA strand exchange or trans-fer procedure as the key point in homologous recom-bination(4,5,10).In earlier studies,the RecA pro-tein in Escherichia coli was identified as the protein catalyzing DNA strand exchange(2,6).Then the DST1and DST2(SEP1)proteins from Saccharomy-ces cerevisiae and the dhp1ϩprotein from Schizosac-charomyces pombe were identified as being involved in this event(1,3,11,9).In addition,the dhp1ϩgene has high homology with the RAT1/TAP1genes from S.cerevisiae and shares a similar function with them in RNA metabolism,including RNA synthesis and RNA trafficking(9).In mammals,the Dhm1and Dhm2genes were cloned and proved to be the true homologues of dhp1ϩand SEP1,respectively,in mouse(7,8).Furthermore,complementation exper-iments revealed that Dhm1could rescue the muta-tion phenotypes of dhp1ϩand SEP1(i.e.,tempera-Sequence data for this article have been deposited with the Gen-Bank Database under Accession No.AF064257.1To whom correspondence should be addressed.Telephone:(86) 21-65642422.Fax:(86)21-65643250.E-mail:longyu@.FIG.1.(A)Homology comparison between human XRN2and mouse DHM1proteins.Identical amino acids are shaded,and simi-lar amino acids are in italics.(B)Region of homology between S. pombe Dhp1ϩand human XRN2proteins.Shadowed bars indicate conserved regions.All articles available online at onGenomics59,252–254(1999)Article ID geno.1999.58662520888-7543/99$30.00Copyright©1999by Academic PressAll rights of reproduction in any formreserved.ture-sensitivity mutation,lethality mutation),suggesting that Dhm1may play a role in homologous recombination and RNA metabolism in mouse (7).To investigate the potential role of the homologous recombination mechanism in humans,we performed a search for homologues in the human EST database and cloned,sequenced,and genetically mapped the cDNA of the human homologue XRN2.With mouse Dhm1cDNA as probe,3196bp of sequence contain-ing a 2850-bp open reading frame that is predicted to encode 950amino acid residues was obtained.Then XRN2cDNA (GenBank Accession No.AF064257)was cloned by performing PCR with a human testis cDNA library (Clontech)as template.Within the coding sequence region,there is 91%homology to mouse Dhm1at the DNA level and 93%identity at the amino acid level (Fig.1A).Similar to the mouse homologue,the N-terminal region (1–405aa)and C-terminal region (509–782aa)have high homology (54and 42%)with the corresponding regions in the Dhp1ϩprotein of S.pombe (Fig.1B).Complementa-tion studies revealed that the two conserved domains can complement the related functions of dhp1ϩand Dhm1,whereas the other regions cannot (7).These findings indicated that the regions could be impor-tant functional domains of the proteins.Northern blot analysis of mRNA revealed a single 3.6-kb transcript in 16adult tissues (Clontech)ex-amined,similar to the Dhm1gene (7).This tran-script was more abundant in testis than in other tissues (Fig.2),suggesting that the gene product may have a function in spermatogenesis,a process that involves mitotic proliferation,meiotic recombi-nation,and sperm maturation.Mouse Dhm1is also expressed highly in liver,whereas the XRN2mes-sage levels are lower in human liver.This result indicates that there may be some difference in the transcriptional regulatory mechanisms of the Dhm1gene and the XRN2gene.By radiation hybrid panel mapping,the human XRN2gene was mapped to chromosome 20p11.1–p11.2.Primers at unique positions (5Ј-AAGCTG-GCTGGAAGCAGCGGTAC-3Ј,1606–1628bp;5Ј-AGTCCTTCAACGTACGACTGCAC-3Ј,1683–1705bp)that amplify a 100-bp DNA band were used to type the Stanford Human Genome Center GB4radi-ation hybrid panel (Research Genetics).In the panel,93radiation hybrid clones were used to detect the presence or absence of this PCR fragment.The hu-man XRN2gene was localized to chromosome 20p11.1–p11.2with very high probability (LOD Ͼ16;the gene is 4.6cR distal to D20S180and 66.8cR proximal to D20S871(Fig.3)).ACKNOWLEDGMENTSThis work was supported by the Chinese 973Program,the Chi-nese 863High Technology Program (863-Z-102-19-04-04),and the National Natural Science Foundation of China (39525015,39680019).REFERENCES1.Clark,A.B.,Dykstra,C.C.,and Sugino,A.(1991).Isolation,DNA sequence,and regulation of a Saccharomyces cerevisiae gene that encodes DNA strand transfer protein.Mol.Cell.Biol.11:2576–2582.2.Cox,M.M.,and Lehman,I.R.(1987).Enzymes of generalrecombination.Annu.Rev.Biochem.56:229–262.3.Dykstra,C.C.,Kitada,K.,Clark,A.B.,Hamatake,R.K.,andSugino,A.(1991).Cloning and characterization of DST2:The gene for DNA strand transfer protein ␤from Saccharomyces cerevisiae.Mol.Cell.Biol.11:2583–2592.4.Holliday,R.(1964).A mechanism for gene conversion in fungi.Genet.Res.5:282–303.5.Meselson,M.S.,and Radding,C.M.(1975).A general model forgenetic A 73:300–304.6.Radding, C.M.(1982).Homologous pairing and strand ex-change in genetic recombination.Annu.Rev.Genet.16:405–437.FIG.2.The expression pattern of XRN2in adult tissues.(A )Northern blots containing mRNA from 16adult human tissues were hybridized with a probe derived from XRN2cDNA.A single 3.6-kb transcript was detected in all tissues with varied expres-sion levels.(B )The same blots were hybridized with ␤-actin cDNA as acontrol.FIG.3.Mapping of XRN2to human chromosome 20p11.1–p11.2.The relationship of XRN2and other markers mapped on the Stan-ford Radiation Hybrid map is shown.The GB42-PT RHMAP pro-gram was used to construct the radiation hybrid map,and the likely order of the markers,centiray distances (cR),and lod scores were determined.253SHORT COMMUNICATION7.Shobuike,T.,Sugano,S.,Yamashita,T.,and Ikeda,H.(1995).Characterization of cDNA encoding mouse homolog offission yeast dhp1ϩgene:Structural and functional conservation.Nu-cleic Acids 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