Characterization and lysine control of expression of the lys1 gene of Penicillium chrysogenum encoding homocitrate synthase

A 2071-bp DNA fragment, containing a gene (lys1) encoding a protein that sh owed 71.1% identical amino acids with the Yarrowia lipolytica homocitrate s ynthase and 71.7% identity with the Saccharomyces cerevisiae homologous enz yme, was cloned from a genomic library of Penicillium chrysogenum. The lys1 gene contained three introns and encoded a protein of 474 amino acids with a deduced molecular mass of 52 kDa. lys1 was located in chromosome II (9.6 Mb) in the wild-type P. chrysogenum NRRL 1951, whereas it hybridized with chromosome III (7.5 Mb) in the high penicillin production strain AS-P-78. T he lys1 gene is transcribed as a monocistronic transcript of 2.0 kb. Levels of the lys1 transcript were high in P. chrysogenum Wis 54-1255 cultures in defined penicillin production medium at 24 and 48 h, coinciding with the r apid growth phase, but dearly decreased during the penicillin production ph ase, suggesting that cc-aminoadipic acid formation for penicillin biosynthe sis may be limited at the homocitrate synthase level. Expression of lys1 wa s partially repressed by high concentrations of lysine in the culture mediu m, but lysine repression seems to be a weak mechanism of control of the lys ine pathway as compared to lysine inhibition of homocitrate synthase. (C) 1 999 Elsevier Science B.V. All rights reserved.