sequence of the debranching enzyme of solanum tuberosum according to the derived oligonucleotide sequences synthetic oligonucleotides are synthesized by standard methods these are used for the scrutiny of genomic dna libraries which represent the genome of solanum tuberosum firstly a genomic dna library is produced according to liu et al 1991 plant mol biol 17 1139 1154 e coli cells of the strain p 2392 are then infected with the phages containing the genomic dna fragments and plated out on medium in petri dishes in a density of 30 000 per cm 2 after ca 8 hours 39 incubation nitrocellulose membranes are laid onto the lysated bacterial lawn which are removed after a minute the filters are incubated for 2 minutes in 0 2 m naoh 1 5 m nacl 2 minutes in 0 4 m tris hcl ph 7 5 then for 2 minutes in 2 fold ssc after drying the fixing of the dna takes place via uv crosslinking the filters are then incubated for 3 hours in a buffer comprising before the radioactively terminally labelled oligonucleotides are added after 12 hours 39 hybridization the filters are washed in 0 2 fold ssc 0 1 sds and then autoradiographed the temperature for hybridization and washing of the filters is calculated as follows suitable oligonucleotide sequences can be calculated from the peptide sequences reproduced in seq id no 1 or seq id no 6 of the debranching enzyme of solanum tuberosum in order to obtain as high as possible a hybridization temperature which guarantees an adequate specifity of the hybridization the longest possible oligonucleotides are to be used however as the length increases so does the degree of degeneracy i e the number of oligonucleotides with different sequence combinations degrees of degeneracy of up to 10.