HnRNP (heterogeneous nuclear ribonucleoprotein) proteins are a group of RNA-binding proteins that play a crucial role in the processing, transport, and translation of mRNA in eukaryotic cells. They bind to pre-mRNA and facilitate the splicing of introns, the processing of 3' and 5' ends, and the assembly of mRNA-protein complexes. HnRNP proteins can form higher order complexes, such as hnRNP:RNA complex sedimenting at 40S, which was identified already almost 60 years ago. The 40S particle is primarily composed of hnRNP C1/2, hnRNP A1/B2, and hnRNP B1/A2 proteins and was hypothesized to play a role in stabilization of pre-mRNA transcripts representing a functional analog of DNA nucleosome. Nevertheless, the exact function and structural arrangement of the 40S still remains elusive. Our aim is to structurally characterize the 40S particle using combination electron cryo-microscopy (cryo-EM) and mass spectrometry data. We have optimized protocols for the purification of A1, C1 and C2 hnRNPs from the bacterial expression system to assemble 40S sub-complexes, particularly the hnRNP C1/C2 tetramer. We have also prepared HEK293 cell lines stably producing labeled hnRNP proteins for purification of the whole 40S particles.