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 has been cloned from the DNA of Aspergillus awamori by hybridization with a probe internal to the KAR2 (BiP) gene of Saccharomyces cerevisiae. The 73.4-kDa-encoded protein showed very high similarity to the endoplasmic reticulum (ER) lumenal BiP protein of S. cerevisiae, Kluyveromyces lactis, Schizosaccharomyces pombe, and animal and plant cells. The BiP protein contains a polar N-terminal end followed by a 18-amino-acid strongly hydrophobic region corresponding to the leader peptide for transport through the ER membrane. In the C-terminal region the protein ends with the HDEL canonical ER retention signal that targets proteins to the lumen of the ER. The A. awamori bip gene contains three introns as shown by cloning and sequencing the putative intron regions from 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 upstream of the first translated ATG were identified by primer extension. The promoter region showed no consensus TATA box but it contains CCAAT and CreA boxes known to be involved in both stress and carbon-catabolite regulation of fungal promoters.