Given the widespread occurrence and extensive conservation of {HEAD ~ the SIR2} like proteins, understanding their molecular mechanism is essential for identifying the cellular roles played by {TAIL ~ these proteins} 
Given the widespread occurrence and extensive conservation of { HEAD ~ the SIR2 } like proteins , understanding their molecular mechanism is essential for identifying the cellular roles played by { TAIL ~ these proteins }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL