Biomaterial Database

Introns in the cytolethal distending toxin gene of Actinobacillus actinomycetemcomitans. 2005

Kai Soo Tan, and Grace Ong, and Keang Peng Song

Microbial Pathogenesis Laboratory, Department of Microbiology, Faculty of Medicine, National University of Singapore, 5 Science Dr. 2, Singapore 117597.

In eukaryotic cells, genes are interrupted by intervening sequences called introns. Introns are transcribed as part of a precursor RNA that is subsequently removed by splicing, giving rise to mature mRNA. However, introns are rarely found in bacteria. Actinobacillus actinomycetemcomitans is a periodontal pathogen implicated in aggressive forms of periodontal disease. This organism has been shown to produce cytolethal distending toxin (CDT), which causes sensitive eukaryotic cells to become irreversibly blocked at the G2/M phase of the cell cycle. In this study, we report the presence of introns within the cdt gene of A. actinomycetemcomitans. By use of reverse transcription-PCR, cdt transcripts of 2.123, 1.572, and 0.882 kb (RTA1, RTA2, and RTA3, respectively) were detected. In contrast, a single 2.123-kb amplicon was obtained by PCR with the genomic DNA. Similar results were obtained when a plasmid carrying cdt was cloned into Escherichia coli. Sequence analysis of RTA1, RTA2, and RTA3 revealed that RTA1 had undergone splicing, giving rise to RTA2 and RTA3. Two exon-intron boundaries, or splice sites, were identified at positions 863 to 868 and 1553 to 1558 of RTA1. Site-directed and deletion mutation studies of the splice site sequence indicated that sequence conservation was important in order for accurate splicing to occur. The catalytic region of the cdt RNA was located within the cdtC gene. This 0.56-kb RNA behaved independently as a catalytically active RNA molecule (a ribozyme) in vitro, capable of splicing heterologous RNA in both cis and trans configurations.

UI	MeSH Term	Description	Entries
D007438	Introns	Sequences of DNA in the genes that are located between the EXONS. They are transcribed along with the exons but are removed from the primary gene transcript by RNA SPLICING to leave mature RNA. Some introns code for separate genes.	Intervening Sequences,Sequences, Intervening,Intervening Sequence,Intron,Sequence, Intervening
D009154	Mutation	Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.	Mutations
D001427	Bacterial Toxins	Toxic substances formed in or elaborated by bacteria; they are usually proteins with high molecular weight and antigenicity; some are used as antibiotics and some to skin test for the presence of or susceptibility to certain diseases.	Bacterial Toxin,Toxins, Bacterial,Toxin, Bacterial
D012329	RNA, Bacterial	Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.	Bacterial RNA
D012333	RNA, Messenger	RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm.	Messenger RNA,Messenger RNA, Polyadenylated,Poly(A) Tail,Poly(A)+ RNA,Poly(A)+ mRNA,RNA, Messenger, Polyadenylated,RNA, Polyadenylated,mRNA,mRNA, Non-Polyadenylated,mRNA, Polyadenylated,Non-Polyadenylated mRNA,Poly(A) RNA,Polyadenylated mRNA,Non Polyadenylated mRNA,Polyadenylated Messenger RNA,Polyadenylated RNA,RNA, Polyadenylated Messenger,mRNA, Non Polyadenylated
D016297	Mutagenesis, Site-Directed	Genetically engineered MUTAGENESIS at a specific site in the DNA molecule that introduces a base substitution, or an insertion or deletion.	Mutagenesis, Oligonucleotide-Directed,Mutagenesis, Site-Specific,Oligonucleotide-Directed Mutagenesis,Site-Directed Mutagenesis,Site-Specific Mutagenesis,Mutageneses, Oligonucleotide-Directed,Mutageneses, Site-Directed,Mutageneses, Site-Specific,Mutagenesis, Oligonucleotide Directed,Mutagenesis, Site Directed,Mutagenesis, Site Specific,Oligonucleotide Directed Mutagenesis,Oligonucleotide-Directed Mutageneses,Site Directed Mutagenesis,Site Specific Mutagenesis,Site-Directed Mutageneses,Site-Specific Mutageneses
D016337	RNA, Catalytic	RNA that has catalytic activity. The catalytic RNA sequence folds to form a complex surface that can function as an enzyme in reactions with itself and other molecules. It may function even in the absence of protein. There are numerous examples of RNA species that are acted upon by catalytic RNA, however the scope of this enzyme class is not limited to a particular type of substrate.	Catalytic RNA,Ribozyme,Ribozymes
D016976	Aggregatibacter actinomycetemcomitans	A species of Gram-negative, facultatively anaerobic spherical or rod-shaped bacteria indigenous to dental surfaces. It is associated with PERIODONTITIS; BACTERIAL ENDOCARDITIS; and ACTINOMYCOSIS.	Actinobacillus actinomycetemcomitans,Bacterium acetinomycetum comitans,Bacterium comitans,Haemophilus actinomyceticomitans,Haemophilus actinomycetemcomitans
D017124	Conserved Sequence	A sequence of amino acids in a polypeptide or of nucleotides in DNA or RNA that is similar across multiple species. A known set of conserved sequences is represented by a CONSENSUS SEQUENCE. AMINO ACID MOTIFS are often composed of conserved sequences.	Conserved Sequences,Sequence, Conserved,Sequences, Conserved
D017384	Sequence Deletion	Deletion of sequences of nucleic acids from the genetic material of an individual.	Deletion Mutation,Deletion Mutations,Deletion, Sequence,Deletions, Sequence,Mutation, Deletion,Mutations, Deletion,Sequence Deletions