A chromosome walk linking the gatA and alcC genes of Aspergillus nidulans

The amdA gene of Aspergillus nidulans has been mapped to linkage group VII, between the gatA and alcC genes ( Jones and SealyLewis 1990 Curr. Genet. 17:81-85). As clones of both of the genes flanking amdA were available, they were used as starting points for chromosome walking towards amdA. The relative orientation of these genes on linkage group VII was not known at the time. Therefore, both walks extended in both directions until overlapping clones from the different walks were detected. The total distance covered by all walks is approximately 240 kb. Creative Commons License This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License. This regular paper is available in Fungal Genetics Reports: http://newprairiepress.org/fgr/vol42/iss1/12 A chromosome walk linking the gatA and alcC genes of Aspergillus nidulans Robyn Lints, Meryl Davis and Michael Hynes Department of Genetics, University of Melbourne, Parkville, 3052 Australia The amdA gene of Aspergillus nidulans has been mapped to linkage group VII, between the gatA and alcC genes (Jones and SealyLewis 1990 Curr. Genet. 17:81-85). As clones of both of the genes flanking amdA were available, they were used as starting points for chromosome walking towards amdA. The relative orientation of these genes on linkage group VII was not known at the time. Therefore, both walks extended in both directions until overlapping clones from the different walks were detected. The total distance covered by all walks is approximately 240 kb. The walk from gatA (encoding GABA transaminase) was initiated using the cosmid clone pGIT1 (Richardson et al. 1989 Mol. Gen. Genet. 217:118-125) and the alcC (encoding alcohol dehyrogenase III) walk was initiated with the plasmid pANa3 (Jones and Sealy-Lewis 1989 Curr. Genet. 17:81-85). The walks were undertaken using an MH2088 (wA3; cbxA1; niiA4; facB88) genomic library in lambdaGEM-11. Lambda clones from all steps were checked against genomic DNA digests to ensure continuity of the walk. In addition, the alcCcontaining cosmids W28:C03, W15:D05 and W7:G02 from the chromosome VII-specific library (Brody et al. 1991 Nucl. Acid. Res. 19:3105-3109) were mapped relative to the early steps of the alcC walk. These cosmid clones and overlapping lambda clones AC6, -7 and -8 contained a repetitive (~5 copies/genome) element of approximately 2 kb. No other repetitive elements were detected in the region of the A. nidulans genome covered by the walk. Overlap of lambda clones was detected when the end fragment of lambda40 (gatA walk) hybridised to the same library plaques (lambdaAC-21, -22 and -23) as end fragments of lambdaAC-18 (alcC walk). Southern blots confirmed that lambdaAC-21, -22 and -23 clones and lambda40 and AC-18 hybridised to common genomic sequences. The linking of the gatA and alcC walks allowed the direction of transcription of these two genes to be orientated relative to each other (see below). The region between the two genes is approximately 130 kb. Complementation studies have shown that the amdA gene lies within a 5 kb BglII fragment of lambdaAC21 (RL, MD and MJH, Mol. Microbiol., in press). Therefore, the known genetic distances between amdA and gatA and between amdA and alcC could be compared with the molecular distances as shown below. The overall value of 15 kb/mu is slightly higher than the overall estimate of 11 kb/mu for chromosome VII, but well within the range of 11.0 24.6 kb/mu across the A. nidulans genome (Brody et al. 1991 Nucl. Acid. Res. 19:3105-3109). The clones from the chromosome walks are available from this laboratory. We acknowledge the support of the Australian Research Council for this work. Published by New Prairie Press, 2017