This can be explained by that fact that the deletion in C fragment of AOX1 gene carried by this strain contains the main binding site for Mxr1 protein which is known tobe the main regulator of MUT genes and is essential for methanol induction .
This region contains one of binding sites for Mxr1 protein and is essential for induction of AOX1 gene in medium with methanol [27, 29, 30].
de la Cruz et al., "Mxr1, a key regulator of the methanol utilization pathway and peroxisomal genes in Pichia pastoris" Molecular and Cellular Biology, vol.
The cDNA was then used as a template in PCR reactions employing Taq DNA polymerase (TaKaRA, Japan) and a pair of primers, MxF1: 5'-AAATGGCTCAAGAGGTGGA-3' and MxR1
: 5'-TATCGCTGACAGTTGGGTG -3', designed based on an EST contig in the NCBI database, and a PCR product of 420 bp was amplified.