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It is widely accepted that expression of most eukaryotic genes is controlled at both transcriptional and post-transcriptional stages. Experimental investigations have revealed a large amount of various signals located in eukaryotic mRNAs (commonly within 5'- or 3'-untranslated regions, UTRs). It has been found that these signals can control expression rate in a tissue-, stress- or developmental stage-specific manner. The analysis of translation signals is rather difficult, because the conformation of mRNA molecule in the cytoplasm may vary depending on the nucleotide sequence and/or the interaction with ubiquitous translational factors or with specific proteins. Elements of the secondary structure may be involved in formation of translational signals, or at least the local secondary structure may affect the signal activity. It is the reason why most posttranscriptional signals remain hidden within mRNA segments of various lengths possessing specific regulatory activities in model experiments. Published data commonly provide description of mRNA elements influencing gene expression pattern in different model constructions and expression systems. Despite this information is generally insufficient for the accurate prediction of a signal it can be beneficial to compare the nucleotide sequence of mRNA of interest with the mRNA sequence seqments possessing regulatory activities.