TRICHODERMA-REESEI SEQUENCES THAT BIND TO THE NUCLEAR MATRIX ENHANCE TRANSFORMATION FREQUENCY

Three DNA fragments, trs1, 2 and 3, isolated from the Trichoderma rees ei genome on the basis of their ability to promote autonomous replicat ion of plasmids in Saccharomyces cerevisiae. Each trs element bound sp ecifically to the isolated T. reesei nuclear matrix in vitro, and two of them bound in vivo, indicating that they are matrix attachment regi ons (MARs). A similar sequence previously isolated from Aspergillus ni dulans (ans1) was also shown to bind specifically to the T. reesei nuc lear matrix in vitro. The T. reesei MARs are AT-rich sequences contain ing 70%, 86% and 73% A + T over 2.9, 0.8 and 3.7 kb, respectively for trs1, 2 and 3. They exhibited no significant sequence homology, but we re shown to contain a number of sequence motifs that occur frequently in many MARs identified in other eukaryotes. However, these motifs occ urred as frequently in the trs elements as in randomly generated seque nces with the same A ST content. trs1 and 3 were shown to be present a s single copies in the T. reesei genome. The presence of the trs eleme nts in transforming plasmids enhanced the frequency of integrative tra nsformation of T. reesei up to five fold over plasmids without a trs. No evidence was obtained to suggest that the trs elements promoted eff icient replication of plasmids in T. reseei. A mechanism for the enhan cement of transformation frequency by the trs elements is proposed.