THE TRANSFORMATION BOOSTER SEQUENCE FROM PETUNIA-HYBRIDA IS A RETROTRANSPOSON DERIVATIVE THAT BINDS TO THE NUCLEAR SCAFFOLD

The transformation booster sequence (TBS) from Petunia hybrida enhances transformation frequencies in P. hybrida, Nicotiana tabacum and Zea mays. TBS also stimulates homologous inter- and intramolecular recombination in P. hybrida, the molecular basis for this stimulation is not known. We investigated whether TBS contains sequence elements that might contribute to the stimulation of recombination and whether its recombinogenic potential reflects a biological function of TBS. We identified a scaffold attachment region (SAR) within TBS and analysed its distribution in the genome and its homologies to other genomic sequences. A 516 bp subfragment of TBS binds to the nuclear scaffold. The sequence of the TBS-SAR fragment shows strong homologies to retroviral elements from plants, suggesting that TBS is an inactive derivative of a retrovirus that still promotes DNA recombination.