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Use of Trinucleotides in Filter Binding (Minimessengers) -

In 1964 Leder and Nirenberg developed a more direct technique for determining codons of amino acids.

This technique employs cellulose nitrate filters and has been called the filter binding technique.

Cellulose nitrate filters were originally used to isolate ribosomes from microorganisms.

The ribosomes are left behind on the filter, while the tRNAs wash through the filter when mRNA is absent.

In the presence of mRNA and ribosomes the tRNAs stick to the filter. mRNA causes binding of amino acid charged tRNA to the ribosomes.

It was found that when the long messengers were substituted by different trinucleotides (triplets) the same results were obtained.

Trinucleotides have been called 'minimessengers', since they consist of only three nucleotides.

Ribosomes were prepared in the filter and different trinucleotide messengers added. If UUD is added to the filter only phenylalanine tRNAs bind to the trinucleotide and are trapped on the filter.

The other amino acids pass through. Similarly, addition of the trinucleotide AAA resulted in lysine tRNA binding to the filter.

Thus by adding specific trinucleotide messengers to the ribosome filter complex and determining the amino acid tRNA bound to the filter the coding pattern can be determined more precisely.