CHARACTERIZATION OF THE BIP GENE OF ASPERGILLUS-AWAMORI ENCODING A PROTEIN WITH AN HDEL RETENTION SIGNAL HOMOLOGOUS TO THE MAMMALIAN BIP INVOLVED IN POLYPEPTIDE SECRETION

A DNA fragment containing an open reading frame of 2016 nucleotides ha s been cloned from the DNA of Aspergillus awamori by hybridization wit h a probe internal to the KAR2 (BiP) gene of Saccharomyces cerevisiae. The 73.4-kDa-encoded protein showed very high similarity to the endop lasmic reticulum (ER) lumenal BiP protein of S. cerevisiae, Kluyveromy ces lactis, Schizosaccharomyces pombe, and animal and plant cells. The BiP protein contains a polar N-terminal end followed by a 18-amino-ac id strongly hydrophobic region corresponding to the leader peptide for transport through the ER membrane. In the C-terminal region the prote in ends with the HDEL canonical ER retention signal that targets prote ins to the lumen of the ER. The A. awamori bip gene contains three int rons as shown by cloning and sequencing the putative intron regions fr om a cDNA library. The bip gene is transcribed as a monocistronic mRNA of 2.4 kb. Two transcription start sites located 160 and 233 bp upstr eam of the first translated ATG were identified by primer extension. T he promoter region showed no consensus TATA box but it contains CCAAT and CreA boxes known to be involved in both stress and carbon-cataboli te regulation of fungal promoters.