7SL RNA

FIGURE 27-33 Directing eukaryotic proteins with the appropriate signals to the endoplasmic reticulum. This process involves the SRP cycle and translocation and cleavage of the nascent polypeptide. The steps are described in the text. SRP is a rod-shaped complex containing a 300 nucleotide RNA (7SL-RNA) and six different proteins (combined Mr 325,000). One protein subunit of SRP binds directly to... 

Archaea contain a stable 7S RNA species of unknown function, which is not associated with the ribosome. The 7S RNA gene from Halobacterium halobium NRC817 has been cloned and sequenced [120]. The sequence resembles the 7SL RNA of eucarya [85] and the 4.5S Escherichia coli) or sc Bacillus subtilis) RNAs of bacteria [121] in potential secondary structure. The 7SL RNA forms part of the signal-recognition particle, involved in protein translocation. The function of the 4.5S RNA is not known exactly, but it is known to be essential [122]. 

The Alu element first appeared tens of millions of years ago and since that time it has been increasing within our genome at the rate of about one copy every 100 years. It is difficult to tell how Alu arose. It shows a striking similarity to a gene (called 7SL RNA) that performs a vital function in our metabolism. But Alu. it seems for rMpw, has no specific function. It is self-serving and, like a parasite, takes advantage of us for ite own replication without... 

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