What is "mt-tt"

Mitochondrially encoded tRNA threonine also known as MT-TT is a transfer RNA which in humans is encoded by the mitochondrial MT-TT gene.

MT-TT is a small 66 nucleotide RNA (human mitochondrial map position 15888-15953) that transfers the amino acid threonine to a growing polypeptide chain at the ribosome site of protein synthesis during translation.