Protein-Coding and Noncoding RNA Genes

Abstract

During the last decade, our understanding about human genes has gradually but drastically changed. When the human genome-sequencing project announced its completion in 2004, they reported the number of human protein-coding genes to be only 20,000–25,000, which was much less than the number that many researchers expected at that time. Later, however, studies on human transcriptome have revealed existence of more transcribed regions of the genome including those without apparent open reading frames, suggesting the existence of many noncoding RNA genes. In the last few years, comprehensive surveys of human proteome on various tissues have successfully validated about 16,000 protein-coding genes at the protein level, but still many candidates of protein-coding genes remained unconfirmed. On the other hand, noncoding RNA genes have attracted more attention, and some of them have been extensively studied for their biological function. It turned out that short noncoding RNAs (ncRNAs) such as miRNAs, snRNAs, and snoRNAs work on posttranscriptional gene silencing and other essential cellular mechanisms, while longer ncRNAs (called lncRNAs) are involve in various biological functions such as chromatin modification, transcription, and splicing. In this chapter, I will describe our current view of these human protein-coding and noncoding RNA genes. In addition, I will illustrate how alternative splicing and other mechanisms diversify human proteome.