Proto-anti-codon RNAs are auto-aminoacylating ribozymes, which are thought to have evolved from any nucleic acid

Nucleic acid

Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...

 molecular system that was capable of forming a hairpin followed by an exposed "anti-codon" sequence and an adjacent step-loop acceptor stem. pacRNAs are postulated as ancestral precursors of proto-tRNAs but are distinguished from tRNAs

Transfer RNA

Transfer RNA is an adaptor molecule composed of RNA, typically 73 to 93 nucleotides in length, that is used in biology to bridge the three-letter genetic code in messenger RNA with the twenty-letter code of amino acids in proteins. The role of tRNA as an adaptor is best understood by...

 in having evolved prior to the evolution of protein translation. The "anti-codon" binding pocket is called an anti-codon because the specific Erives

Albert Erives

Albert Erives is a professor at Dartmouth College known for the pacRNA model for the joint origin of the genetic code and universal homochirality. He is also known for several findings in developmental biology and gene regulation....

 model of pacRNAs predicts many of the anti-codon sequences of the genetic code. The pacRNA model is also thought to provide a key explanation for the origins of homochirality

Homochirality

Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. Molecules involved are not necessarily the same compound, but similar groups are arranged in the same way around a central atom. In biology homochirality is found in the chemical building blocks...

, or at least of complementary homochiralities between amino acids and nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 sequneces.

Aminoacylated RNA world

pacRNAs are thought to represent the key molecular entities during an extensive aminoacylated RNA world. The pacRNA model holds that early RNA world was predominantly an aminoacylated RNA world.