Martin R
Krebs Institute for Biomolecular Research, University of Sheffield, Western Bank, UK.
Nucleic Acids Res. 1994 Jan 11;22(1):15-9. doi: 10.1093/nar/22.1.15.
The nucleotide sequences 3' to the translational termination codons in a collection of human genes have been analysed for evidence of a preferred 3' context for natural UAG codons. The aim was to see whether human UAG contexts can be related to the recent demonstration of the effects of 3' context on nonsense suppression in human cells. Since mammalian genomes are known to consist of a patchwork of blocks of sequences or 'isochores' with different G+C contents, the collection of genes was split into 5 classes containing genes with similar frequencies of G+C at the 3rd position of synonymous codons. This analysis revealed that the frequency of bases 3' to UAG varies with the G+C frequency of the gene, and that these changes were mirrored by changes in the patterns of bases in GN and AGN strings. The identity of the next 3' base appears therefore to be determined by genome wide changes in G+C composition, rather than selection to maintain a particular tetranucleotide stop signal. These findings argue strongly that the failure to find bias in the patterns of bases used in human coding sequences is an insensitive guide for the existence of codon usage or codon context effects during translation in human cells.
已对一组人类基因中翻译终止密码子下游的核苷酸序列进行分析，以寻找天然UAG密码子偏好性3'上下文的证据。目的是探究人类UAG上下文是否与最近关于3'上下文对人类细胞无义抑制作用的研究结果相关。由于已知哺乳动物基因组由具有不同G+C含量的序列块或“等密度区带”拼凑而成，因此将该组基因分为5类，每类基因在同义密码子第3位的G+C频率相似。该分析表明，UAG下游碱基的频率随基因的G+C频率而变化，并且这些变化反映在GN和AGN序列的碱基模式变化中。因此，下一个3'碱基的身份似乎由全基因组G+C组成的变化决定，而非由维持特定四核苷酸终止信号的选择决定。这些发现有力地表明，在人类编码序列中未发现碱基模式偏差，并不能作为判断人类细胞翻译过程中密码子使用或密码子上下文效应是否存在的可靠依据。
