The correct interpretation — that this RNA played the role of a messenger between the inserted phage DNA and the appearance of viral proteins in the bacterial cell — was provided by Jacob and Monod. Nevertheless, understanding regulation of important eukaryotic proteins requires that messenger RNAs (mRNAs) be isolated from higher organisms. A polysome consists of mRNA to which several ribosomes are attached, each bearing a nascent polypeptide chain whose length depends on how much of the cistronic template has been read during translation. Since most tissues synthesize many proteins at any given time, the isolated polysomes contain a variety of mRNAs. Total nucleic acid extraction has also been used in the preparation of mRNA for the small subunit of RuBPCase. Preliminary evidence suggested the cDNA, synthesized from the 9S leghemoglobin mRNA hybridized with plant DNA, essentially confirming that leghemoglobin is indeed a gene for a plant protein.