| Definition |
A gene trap cassette is designed to interrupt transcription of an endogenous locus upon integration of the cassette into the genome. The basic components of a gene trap cassette are a promoterless gene with an upstream splice acceptor site. Upon integration into an intron, splicing from the genomic splice donor site to the splice acceptor site in the cassette results in a transcriptional fusion containing the endogenous exon(s) upstream of the insertion fused to the gene sequence encoded by the cassette. Any open reading frame (ORF) encoded by the trap cassette gene may be translated from this transcriptional fusion either as a translational fusion with any ORF sequence encoded by the upstream exons, or if an internal ribosome entry site (IRES) or viral 2A-like peptide sequence (which promotes ribosome skipping) is present upstream of the gene trap ORF, it may be produced as a separate protein expressed under the control of the regulatory sequences of the endogenous locus. Gene trap insertions are usually mutagenic, disrupting the locus into which they have inserted, since termination sequences are usually present at the 3' end of the cassette, truncating the endogenous transcript. Depending on the nature of the gene encoded by the gene trap cassette, a gene trap insertion may directly report the expression pattern of the disrupted locus (e.g. if it encodes a reporter enzyme or fluorescent protein), or it may be used to drive expression of any gene of interest in the pattern of the trapped locus (e.g. if it is a driver that forms part of a binary expression system). A gene trap cassette may be inserted into a genome as part of a transgenic construct via transposable-element-mediated transgenesis, or may be inserted directly into a modified endogenous locus via a genome engineering method such as homologous recombination or CRISPR.[ PubMed:10899970 ] |
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