%0 Journal Article
%T Mutations in the Lactococcus lactis Ll.LtrB group II intron that retain mobility in vivo
%A Lisa M D'Souza
%A Jin Zhong
%J BMC Molecular Biology
%D 2002
%I BioMed Central
%R 10.1186/1471-2199-3-17
%X The largest deletion that could be made without severely compromising mobility was 158 nucleotides in DIVb(1¨C2). This mutant had a mobility frequency comparable to the wild-type Ll.LtrB intron (¦¤ORF construct). Hence, all subsequent mutations were done in this mutant background. Deletion of DIIb reduced mobility to approximately 18% of wild-type, while another deletion in domain II (nts 404¨C459) was mobile to a minor extent. Only two deletions in DI and none in DIII were tolerated. Some mobility was also observed for a DIVa deletion mutant. Of the three point mutants at position G3 in DV, only G3A retained mobility. In DVI, deletion of the branch-point nucleotide abolished mobility, but the presence of any nucleotide at the branch-point position restored mobility to some extent.The smallest intron capable of efficient retrohoming was 725 nucleotides, comprising the DIVb(1¨C2) and DII(ii)a,b deletions. The tertiary elements found to be nonessential for mobility were alpha, kappa and eta. In DV, only the G3A mutant was mobile. A branch-point residue is required for intron mobility.Group II introns are catalytic RNAs that are also mobile genetic elements. Although their primary sequences vary considerably, the intron RNAs fold into well-conserved structures (Figure 1). The generalized group II intron secondary structure consists of six helical domains emerging from a central wheel [1,2]. Some group II introns are capable of self-splicing; however for efficient splicing in vivo, the intron-encoded ORF or host-encoded splicing factors are required [3]. Mobile group II introns encode a reverse transcriptase/maturase, with the coding region generally located in domain IV.Group II introns were first identified in fungal mitochondria and grouped on the basis of their secondary structures [2,4,5]. They have been found in organelle genomes of fungi and plants and also in a number of bacteria [6]. None have been found in animals, although it has been suggested that group II intr
%U http://www.biomedcentral.com/1471-2199/3/17