Translational Regulation of Connexins
The transcriptional control constitutes a major step in the regulation of gene expression. However, proteins are the major cell entities that act as the actual business ends of the cell physiology. The transcriptional regulation of gene expression is just an initial step in the formation of proteins. Translation of mRNAs into proteins constitutes another important step in regulating the expression of proteins. For the proper functioning of a cell, the functional entities, which include the proteins, must be present at a defined concentration, at a particular time, and at a proper location. At a particular time, cells possess thousands of mRNA molecules, each competing for the components of translational machinery. Thus to avoid such competition, it becomes imperative for a cell to regulate the translation of its different mRNAs. Moreover, cells are always exposed to varying conditions, and for its survival, it needs to respond properly and in a particular period. Regulation at the transcriptional level takes some time, while regulation at the translational level is a rapid and more direct one. Thus, translational regulation gives a cell the required adaptability to respond to the changing conditions. Translational regulation can occur at multiple steps, like initiation, elongation, and degradation. Regulation at the initiation step is the most critical one, and this allows for the precise spatial and temporal fine-tuning of protein levels to permit normal physiological function. The regulation of connexin translation can be studied at two levels. One is cap-dependent and another is cap-independent translation. The role of these two means of translational regulation of connexin expression is discussed below.