termination signal : The intrinsic terminator sequence An inverted repeat of GC-rich sequence followed by 4 or more adenines . The transcribed RNA forms stem-loop structure at inverted repeats via internal base pairing The formation of this stem-loop structure disrupts hydrogen bonding between RNA uracils and DNA adenines at site of transcription (weak because only 2 H-bonds between A and U as compared to 3 between G and C) As a result, RNA is released from the DNA template What is an inverted repeat ? A sequence of several bases in double-stranded DNA that is repeated in an inverted fashion Example : • 5'. ....GCCAGTGG. ....... CCACTGGC. ...3' • 3'. ....CGGTCACC. ....... GGTGACCG. ...5' ( template strand ) transcribed RNA : 5'. ...... GCCAGUGG. ...... CCACUGGC. ....3' Consequently there are internal sequences in the transcribed RNA that are complementary and can therefore base pair to form a stem-loop structure Some termination sequences lack the series of adenines which are transcribed in to
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This document was uploaded on 11/03/2011 for the course BIOLOGY MCB2010 at Broward College.