plasmid which had been treated with the same enzymes the plasmids which have been constructed in this way contain the complete meta gene possessing a sequence at codon 294 or respectively 101 which is in each case altered as compared with the wild type sequence thereby making it possible to use them to produce different homoserine transsuccinylase variants table 1 the activity and the influence of l methionine on the activity of the different homoserine transsuccinylases were determined by means of an enzyme test using cell extracts in which the respective proteins had been produced for this the corresponding plasmids encoding altered homoserine transsuccinylases were introduced by transformation into the e coli strain w3110 atcc 27325 using methods known to the skilled person the transformation mixture was spread on lb tetracycline agar plates 10 g of tryptone l 5 g of yeast extract l 5 g of nacl l 15 g of agar l and 15 mg of tetracycline l and incubated at 37 u00b0 c overnight the resulting transformants were grown in sm1 medium for 1 l of medium cacl 2 u00d7 2h 2 o 0 0147 g mgso 4 u00d7 7h 2 o 0 3 g na 2 moo 4 u00d7 2h 2 o 0 15 mg h 3 bo 3 2 5 mg cocl 2.