Gene Splicing

Genes are DNA sequences that code for protein. Gene splicing is a form of genetic engineering where specific genes or gene sequences are inserted into the genome of a different organism. Gene splicing can also specifically refer to a step during the processing of deoxyribonucleic acid (DNA) to prepare it to be translated into protein.

Gene splicing can also be applied to molecular biology techniques that are aimed at integrating various DNA sequences or gene into the DNA of cells. Individual genes encode specific proteins and it is estimated that there are approximately 50,000 genes in each cell of the human body. Because the cellular functions in different tissues have varying purposes, the genes undergo a complex concerted effort to maintain the appropriate level of gene expression in a tissue specific manner. For example, muscle cells require specific proteins to function, and these proteins differ remarkably from proteins in brain cells. Although the genetic information is, for the most part, the same in both cell types, the different functional purposes result in different cellular needs and therefore different proteins are produced in different tissue types.

Genes are not expressed without the proper signals. Many genes can remain inactive. With the appropriate stimulation of gene expression, the cell can produce various proteins. The DNA must first be processed into a form that other molecules in the cell can recognize and translate it into the appropriate protein. Before DNA can be converted into protein, it must be transcribed into ribonucleic acid (RNA). There are three steps in RNA maturation; splicing, capping, and polyadenylating. Each of these steps are involved in preparing the newly created RNA, called the RNA transcript, so that it can exit the nucleus without being degraded. In terms of gene expression, the splicing of RNA is the step where gene splicing occurs in this context at specific locations throughout the gene. The areas of the gene that are spliced out are represent noncoding regions that are intervening sequences also known as introns. The DNA that remains in the processed RNA is referred to as the coding regions and each coding regions of the gene are known as exons. Therefore, introns are intervening sequences between exons and gene splicing entails the excision of introns and the joining together of exons. Hence, the final sequence will be shorter than the original coding gene or DNA sequence.

In order to appreciate the role splicing plays in how genes are expressed, it is important to understand how a gene changes into its functional form. Initially, RNA is called precursor RNA (or pre-RNA). Pre-RNAs are then further modified to other RNAs called transfer RNA (tRNA), ribosomal RNA (rRNA), or messenger RNA (mRNA). mRNAs encode proteins in a process called translation, while the other RNAs are important for helping the mRNA be translated into protein. RNA splicing creates functional RNA molecules from the pre-RNAs.

Splicing usually proceeds in a predetermined way for each gene. Experiments which have halted transcript formation at different intervals of time show that splicing will follow a major pathway beginning with some intron and proceeding selectively to another, not necessarily adjacent, intron. Although other pathways can be followed, each transcript has its own primary sequence for intron excision.