Short Interspersed Nucleotide Elements, or SINEs, are small DNA sequences that are found in eukaryotic genomes. The spelling of this term uses the IPA phonetic transcription to help clarify its pronunciation: /ʃɔːrt ɪntərˈspɜːst ˈnjuːkliətaɪd ˈɛlɪmənts/. This means that the "sh" sound at the beginning of the first word is pronounced as in "sheep," while the second word has emphasis on the second syllable with a short "i" sound. The final two words are pronounced with emphasis on the first syllable and a long "i" sound in "nucleotide."
Short Interspersed Nucleotide Elements (SINEs) are a type of repetitive DNA sequence found within genomes. They are one of the two main classes of transposable elements, the other being Long Interspersed Nucleotide Elements (LINEs). SINEs are characterized by their relatively short size, typically ranging from 100 to 1,000 base pairs in length.
SINEs are interspersed throughout the genome, meaning they are distributed randomly among other DNA sequences rather than being concentrated in specific clusters. They are typically non-coding DNA, meaning they do not contain instructions for producing proteins. However, they can occasionally have regulatory roles, influencing the expression of nearby genes.
The structure of SINEs consists of a central region that varies in sequence and may be derived from RNA, surrounded by repetitive sequences known as terminal inverted repeats (TIRs) on either side. These TIRs enable SINEs to be recognized and inserted into new genomic locations by specific enzymes called transposases.
SINEs are present in the genomes of many organisms, including humans. The most well-known SINE in humans is the Alu element, which is approximately 300 base pairs long and makes up around 10% of the human genome. SINEs have been implicated in various genetic phenomena, including genomic rearrangements, gene regulation, and the evolution of new genes. Their repetitive nature and ability to copy themselves contribute to the overall complexity and plasticity of genomes.