Binds specifically to cytosolic chaperonin (c-CPN) and transfers target proteins to it (PubMed:19825635). Binds to nascent polypeptide chain and promotes folding in an environment in which there are many competing pathways for nonnative proteins (PubMed:19825635). Together with other chaperonins, contribute to the regulation of gene expression by modulating the spliceosome function on pre-mRNA splicing post-transcriptionally by acting as a co-chaperone of Hsp90 to control levels of LSM8, especially in cold conditions (PubMed:32396196). Required for microtubules (MTs) (MTs) organization and dynamicity (PubMed:19004800, PubMed:28412546). Involved in the process leading to microtubules dissociation in response to gibberellic acid (GA) probably due to the DELLA proteins-mediated translocation of the prefoldin co-chaperone complex from the cytoplasm to the nucleus (PubMed:28412546). Prevents cold acclimation (e.g. 7 days at 4 degrees Celsius) in a DELLA proteins-dependent manner by promoting nuclear proteasome-mediated HY5 degradation, thus modulating the expression of several genes and reducing anthocyanin biosynthesis, but seems not involved in constitutive freezing tolerance (PubMed:28412546). Heterohexamer of two PFD-alpha type and four PFD-beta type subunits forming prefoldin co-chaperone complex (By similarity). Interacts with ABI3 (via C-terminus) (PubMed:10743655). Interacts with PFD6 (PubMed:19004800). Binds to HY5 in the nucleus and at low temperature (e.g. at 4 degrees Celsius) (PubMed:28412546). Interacts with LSM8, a specific subunit of the LSM2-8 complex, which is a core component of the spliceosome (PubMed:32396196). Binds to HSP90 to facilitate the formation of a larger complex made at least of HSP90, PFD4 and LSM8 (PubMed:32396196). In the presence of gibberellic acid (GA) and at room temperature, the prefoldin complex stays in the cytoplasm and is functional (PubMed:28412546). But in the absence of GA or in response to cold, the prefoldin complex is localized to the nucleus in the presence of DELLA proteins, which severely compromises alpha/beta-tubulin heterodimer availability, thus affecting microtubules (MTs) organization (PubMed:28412546). This changing subcellular localization follows a daily rhythm coordinated oscillation (By similarity). Accumulates in response to cold (PubMed:28412546, PubMed:32396196). Reduced levels upon treatment with geldanamycin (GDA), a Hsp90 inhibitor (PubMed:32396196). Hypersensitivity to oryzalin (a microtubule inhibitor) (PubMed:19004800). Increased sensitivity to high salt treatment (PubMed:32396196). Smaller plants due to reduced cells size and associated with lower levels of both alpha and beta tubulin subunits, as well as highly disorganized cortical microtubules (MTs) (PubMed:28412546, PubMed:32396196). Increased capacity to tolerate freezing temperatures upon acclimation (e.g. 7 days at 4 degrees Celsius) associated with a continuous accumulation of HY5 in cold conditions, characterized by a lower ubiquitination status (PubMed:28412546). Reduced levels of LSM8 and of LSM2-8 complex via a post-transcriptional process, especially in cold conditions (at protein level) (PubMed:32396196). Slightly reduced production of U6 snRNA at room temperature, but to higher extent in cold situation (PubMed:32396196). Lower pre-mRNA splicing events and reduced production of U6 snRNA in plants lacking PFD2, PFD4 and PFD6, probably due to a reduced activity of the LSM2-8 complex (PubMed:32396196). Belongs to the prefoldin subunit beta family. Intron retention.