Genetic code reading frames

FIGURE 27-5 Reading frames in the genetic code. In a triplet, nonoverlapping code, all mRNAs have three potential reading frames, shaded here in different colors. The triplets, and hence the amino acids specified, are different in each reading frame. 

FRAMESHIFT MUTATION A gene mutation that occurs by the addition or deletion of one or a few base pairs and causes a shift in the reading frame of the genetic code, thereby altering the message encoded by all DNA base pairs that are read after the point of the mutation. 

The EDITSEQ application allows you to manually enter DNA or protein sequence information into your computer. This application has several features that make it useful to the research scientist. First, it can identify open reading frames (possible gene sequences) within a DNA sequence. Second, it can provide the percent base composition (A,G,C,T), the percent GC, the percent AT, and the melting temperature of the entire sequence or a small subset of that sequence. Third, EDITSEQ can translate a nucleotide sequence into a protein sequence. Finally, the application is capable of translating or reverse translating a nucleotide sequence of interest using codes other than the standard genetic code. 

Consequently, they lead to the insertion or deletion of one or more base pairs. The effect of such mutations is to alter the reading frame in translation, unless an integral multiple of three base pairs is inserted or deleted. In fact, the analysis of such mutants contributed greatly to the revelation of the triplet nature of the genetic code. 

Translated BLAST searches use a genetic code to translate either the query, database subjects, or both, into protein sequences, which are then aligned as in blastp. The translations are performed in the three forward as well as the three reverse reading frames so that no possible translation is missed. 

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