Specific encapsidation of TMV RNA fragments by 25S TMV protein: Isolation and some properties of the nucleoprotein complexes formed

Abstract

25 S TMV protein, when added to a mixture of TMV RNA fragments obtained by partial T 1 RNase digestion, is able to recognize only a few species of RNA fragments, all of them deriving from an unique sequence of 103 nucleotides that represents a part of the coat protein cistron. This selective encapsidation leads to the formation of two types of stable nucleoprotein complexes. These complexes have sedimentation coefficients of 26 and 34 S, contain about half the amount of RNA than native TMV and are resistant to pancreatic ribonuclease. Added to a mixture of intact TMV RNA and 25 S TMV protein, the specifically encapsidated RNA fragments (SERF) extracted from the 26 and 34 S particles induce a rapid inhibition of the reconstitution process as shown by light scattering measurements. This inhibition due to the rapid encapsidation of SERF by 25 S TMV protein, demonstrates that TMV protein has a great affinity for SERF even in the presence of native TMV RNA. The affinity is specific since other polynucleotides such as poly(A) or tRNA do not cause the same inhibitory effect, i.e., they do not compete with TMV RNA for 25 S TMV protein.