I have problem with yeast transformation. I tried to transform pyes3-tryp(my insert inside) into INVsc1 yeast cell by following the protocol in the manual for few times but failed(confluent with growth). In the manual, it states :INVSc1 will not grow in SC minimal medium that is deficient in histidine, leucine, tryptophan, or uracil.I tried 2 media: selective media+ amino acids except tryp and selective media + amino acids except the 4 amino acids. There are confluent growths, no single colony on both of the plates including on the negative control plate( only yeast cell no plasmid).However, the confluent growth is less severe in the plate without the 4 amino acid. Everything i used is sterile except the old DMSO in my lab which had been opened outside of the laminar before. So, is it due to contamination by bacteria or...??.