Abstract: A method for screening substances that inhibit binding between a TAK1 polypeptide and a TAB1 polypeptide, which comprises contacting the TAB1 polypeptide to the TAK1 polypeptide and a test sample and then detecting or determining the TAK1 polypeptide that is bound to the TAB1 polypeptide.

Abstract: A method for isolating a ribonucleic acid, which comprises dissolution of a sample containing the ribonucleic acid, such as cells, in an acidic solution containing a lithium salt and a chaotropic agent, bringing the ribonucleic acid into contact with a nucleic acid-binding carrier such as silica particles, thereby to allow selective adsorption of the ribonucleic acid alone onto said carrier, and eluting the ribonucleic acid from the nucleic acid-bound carrier; a reagent therefor; and a method for producing a cDNA from the ribonucleic acid isolated by this method. According to the present invention, a high purity ribonucleic acid can be isolated quickly and safely from a sample containing the ribonucleic acid.