Cloning, mapping and characterization of a genomic copy of the Lipomyces kononenkoae α-amylase-encoding gene (LKA1)
The expression in Saccharomyces cerevisiae and Schizosaccharomyces pombe of a cDNA copy of the Lipomyces kononenkoae IGC4052B α-amylase gene (LKA1), linked to the phosphoglycerate kinase gene (PGK1) promoter, resulted in the extracellular production of biologically active α-amylase (LKA1). However, transformation of S. cerevisiae and Schiz. pombe with a cosmid clone containing the complete genomic copy of LKA1, expressed from its native promoter, did not result in secretion of active α-amylase by any of the transformants. When the cDNA copy of LKA1 was expressed in S. cerevisiae under control of the wild-type L. kononenkoae promoter, biologically active α-amylase was secreted into the culture medium, indicating the recognition of the LKA1 promoter in S. cerevisiae. Sequence analysis of the GC-rich LKA1 promoter revealed canonical sequences that are homologous to the TATAAA, CAAT and CCAAT boxes and GCN4-binding sites that are present in several promoter sequences of S. cerevisiae. Primer extension analysis of LKA1 transcripts in L. kononenkoae indicated major initiation sites at nucleotides -64 and -65. S. cerevisiae and Schiz. pombe cells transformed with a plasmid containing the open reading frame of the genomic copy of LKA1, linked to the PGK1 promoter, did not produce α-amylase. Polymerase chain reaction mapping and sequence analysis revealed the presence of a 61-bp intron in the genomic copy of LKA1 that impaired synthesis of biologically active α-amylase in S. cerevisiae and Schiz. pombe. This intron contains donor, acceptor and branch sequences that correlate with the consensus sequences identified in the introns of split genes from Schiz. pombe and mammals. Pulsed-field gradient gel electrophoresis resolved at least eight chromosomal DNAs for L. kononenkoae IGC4052B and chromoblot analysis indicated that LKA1 is located on the second smallest chromosome, designated chromosome II.