mRNA-binding protein that acts as a regulator of mRNAs transport, translation and/or stability, and which is involved in neurogenesis, synaptic plasticity in neurons and cell proliferation and migration in multiple cell types (PubMed:17210633, PubMed:31439799, PubMed:35979925). Plays an essential role in cytoplasmic stress granule formation (PubMed:35977029). Acts as an mRNA regulator by mediating formation of some phase-separated membraneless compartment: undergoes liquid-liquid phase separation upon binding to target mRNAs, leading to assemble mRNAs into cytoplasmic ribonucleoprotein granules that concentrate mRNAs with associated regulatory factors (PubMed:31439799, PubMed:32302570, PubMed:32302571, PubMed:32302572, PubMed:34074792, PubMed:36040869, PubMed:36279435). Undergoes liquid-liquid phase separation following phosphorylation and interaction with FMR1, promoting formation of cytoplasmic ribonucleoprotein granules that concentrate mRNAs with factors that inhibit translation and mediate deadenylation of target mRNAs (PubMed:31439799). In these cytoplasmic ribonucleoprotein granules, CAPRIN1 mediates recruitment of CNOT7 deadenylase, leading to mRNA deadenylation and degradation (PubMed:31439799). Binds directly and selectively to MYC and CCND2 mRNAs (PubMed:17210633). In neuronal cells, directly binds to several mRNAs associated with RNA granules, including BDNF, CAMK2A, CREB1, MAP2, NTRK2 mRNAs, as well as to GRIN1 and KPNB1 mRNAs, but not to rRNAs (PubMed:17210633). {ECO:0000269|PubMed:17210633, ECO:0000269|PubMed:31439799, ECO:0000269|PubMed:32302570, ECO:0000269|PubMed:32302571, ECO:0000269|PubMed:34074792, ECO:0000269|PubMed:35977029, ECO:0000269|PubMed:35979925, ECO:0000269|PubMed:36040869, ECO:0000269|PubMed:36279435}. This is the function of CAPRIN1 (cell cycle associated protein 1, Ensembl gene identifier ENSG00000135387).