A defective non-LTR retrotransposon is dispersed throughout the genome of the silkworm, Bombyx mori

Abstract

The presence of long repetitive sequences is demonstrated in the genome of the silkworm, Bombyx mori. Members of this BMC1 family reveal several features typical of the L1 (long interspersed sequence one) family of mammals, except for species specific elements. The number of BMC1 elements is estimated to be approximately 3500 per haploid genome. Elements containing the full length unit of 5.1 kb are dispersed throughout the genome and their restriction sites are conserved, although most members are preferentially truncated to varying extents at their 5' ends. DNA sequencing indicates that this element contains six tandem repeats of 15 bp CpG-rich sequence in the 5' proximal region. It terminates with a 3' oligo(A) stretch, and is flanked at both ends by a 7-10 bp target sequence duplication. In addition, there is significant evidence for amino acid sequence homology with reverse transcriptase domains of other L1 families, especially F, Doc and Jockey of Drosophila melanogaster. No large open reading frame is present. The BMC1 element is suggested to be dispersed in the genome by a transposition mechanism involving RNA intermediates.

Cloning and characterization of a mariner-like element in the silkworm, Bombyx mori.

“…Why so many larger products were amplified is a very interesting subject when considering the actual function of BmMLEs. According to Maekawa (personal communication), the 4.2-kb BmMLE is interrupted by the insertion of a short retroposon containing the nonLTR retrotransposable element, BMC1 (Ogura et al, 1994). In our clone, the ORF was also inactivated by an LTR retrotransposable like sequence.…”

“…In silkworms, many other kinds of transposable elements have been reported. However, most of them belong to Class I (Eickbush, 1995;Ogura et al, 1994), although one type of Class II transposable element with no ORF has been reported (Ueda et al, 1986). To develop a vector for transgenesis in the silkworm, a new type of transposable element of Class II would be very important.…”

Molecular structure of the copia-like retrotransposable element Yokozuna on the W chromosome of the silkworm, Bombyx mori.

“…Based on a blastn and a blastx search, we determined that this 18.1-kb insertional DNA is composed primarily of clusters of three retrotransposable elements, one retroposon, and one functionally unknown insertion. Each element, namely a non-LTR retrotransposable element BMC1 (Ogura et al, 1994), a retroposon Bm1 (Adams et al, 1986), functionally unknown inserted DNA (designated as FUI), and a novel copia-like LTR retrotransposable element, Yokozuna, was inserted into a novel gypsy-Ty3-like LTR retrotransposable element, Kabuki (unpublished) (Fig. 2).…”

Identification of novel random amplified polymorphic DNAs (RAPDs) on the W chromosome of the domesticated silkworm, Bombyx mori, and the wild silkworm, B. mandarina, and their retrotransposable elementrelated nucleotide sequences.

“…We analyzed 28 RAPD sequences amplified from the autosomes and the Z chromosome of B. mori. Among 28 RAPD sequences, six did not contain an amino acid coding region; 14 showed homology with Bm1, Bm2 (retroposons; approximately 5% of the B. mori genome is composed of Bm1 [Eickbush, 1995]) and BMC1 (a non-long terminal repeat [LTR] retrotransposable element of which 1-2% of the B. mori genome is composed [Ogura et al,1994;Eickbush, 1995]); and eight RAPD sequences that contain partial amino acid coding regions, of which only one showed relatively strong homology with the amino acid sequence of transposon Minos of D. melanogaster (data not shown). Thus, it is not likely that almost all RAPD sequences amplified from genomic DNA of B. mori show homology to retrotransposable elements.…”