Plays an essential role in the assembly of two types of T4P pili: a wide and a narrow that participate in natural transformation and twitching motility (PubMed:32376942). Major component of the wide pilus that is essential for natural transformation working as a DNA translocator structure that spans the inner and outer membranes (PubMed:12839734, PubMed:19396940, PubMed:32376942, PubMed:16857013). In addition, participates in the assembly of the narrow pilus composed of the PilA5 subunit that is required for twitching motility (PubMed:32376942). Interacts with PilQ. The single N-terminal transmembrane is initially involved in the correct localization to the inner membrane. Once the leader sequence cleaved, this region plays a role in multimerization and protein-protein interactions in the periplasm and the outer membrane. By growth in minimal medium or low temperature leading to a significant increase in pilA4 transcripts. Found in three forms of 14-kDa, 18-kDa and a glycosylated 23-kDa form (PubMed:16857013). Both narrow and wide pili are glycosylated (PubMed:32376942). Deletion mutants show defect in both DNA transformation and twitching motility.