A novel maT-type transposable element, BmamaT1, in Bombyx mandarina, homologous to the B. mori mariner-like element Bmmar6

Abstract

A complex type marner-like element (MLE) was isolated by PCR with genomic DNA of Bombyx mandarina. The clones of this MLE, homologous to the ‘Cecropia-ITR-MLE’ in BmTNML locus that we have isolated previously from B. mori, were roughly classified into four groups according to the state of inserted elements: (1) Containing a retrotransposon (L1Bm) and another element, (2) containing L1Bm alone, (3) containing another element alone and (4) without insertions. This inserted element was named BmamaT1, as it was homologous to the B. mori MLE called Bmmar6, which was previously reported to be similar to a maT-family member, Bmmar1. Many of the current Cecropia-ITR-MLE clones had, as the BmamaT1 insertion site, the sequence of TA/TATA, which may be a transposition target site. Moreover, the BmamaT1 elements that inserted into the Cecropia-ITR-MLE region were highly homogeneous, making one group when a phylogenetic tree was made together with BmamaT1 members isolated directly from the B. mandarina genome. Many of the inserted type BmamaT1 elements had complete ORF which possessed the so-called DDD catalytic triad. All these findings were taken to indicate that a large fraction of the BmamaT1 elements are still highly active.