Mass spectrometry approach to identify mitochondrial poly(A) RNA interacting proteins

To identify mitochondrial RNA-interacting proteins, we developed three related mass spectrometry based methods. In the first method, called mitochondrial crosslinking (MXL), mitochondria of 4-thiouridine labelled cells were isolated, exposed to UV-light and poly(A) RNA was isolated. In the second method, called whole cell crosslinking (WCXL), 4-thiouridine labelled cells were first exposed to UV-light, subsequently mitochondria were isolated followed by a poly(A) RNA extraction. The third method, called ethidium bromide whole cell crosslinking (WCXL_EtBr), is exactly the same as the WCXL method, but the cells are cultured with ethidium bromide to reduce the amount of mitochondrial RNA. In all methods poly(A) RNA was degraded and proteins in the sample were digested and identified using mass spectrometry.