CLONING OF A CDNA FROM ARABIDOPSIS-THALIANA HOMOLOGOUS TO THE HUMAN XPB GENE

The human gene XPB, defective in xeroderma pigmentosum patients comple mentation group B, encodes a DNA helicase involved in several DNA meta bolic pathways, including DNA repair and transcription. The high conse rvation of this gene has allowed the cloning of homologs in various sp ecies, such as mouse, yeast and Drosophila. Not much information on th e molecular basis of nucleotide excision repair in plants is available , bur these organisms may have similar mechanisms to other eukaryotes. A homolog of XPB was isolated in Arabidopsis thaliana by using polyme rase chain reaction (PCR) with degenerate oligonucleotides based on pr otein domains which are conserved among several species. Screening of an Arabidopsis cDNA library led to the identification and isolation of a cDNA clone with 2670 bp encoding a predicted protein of 767 amino a cids, denoted araXPB. Genomic analysis indicated that this is a nuclea r single copy gene in plant cells. Northern blot with the cDNA probe r evealed a major transcript which migrated at approx. 2800 b, in agreem ent with the size of the cDNA isolated. The araXPB protein shares appr oximately 50% identical and 70% conserved amino acids with :he yeast a nd human homologs. The plant protein maintains all the functional doma ins found in the other proteins, including nuclear localization signal , DNA-binding domain and helicase motifs, suggesting that it might als o act as part of the RNA transcription apparatus, as well as nucleotid e excision repair in plant cells. (C) 1998 Elsevier Science B.V.