RNA binding protein that regulates various processes including circadian behaviors, actin filament formation, eye development and oocyte formation (PubMed:12524342, PubMed:28388438). Forms a complex with tyf and pAbp which functions in adult circadian pacemaker neurons to sustain circadian rhythms likely by switching between activator and repressor modes of post-transcriptional regulation via interaction with Lsm12a or me31B (PubMed:28388438). Forms an activator complex (Atx2-tyf activator complex) via association with Lsm12a and activates the TYF-dependent translation of per to maintain 24 hour periodicity in circadian locomotor behaviors (PubMed:28388438). Forms a repressor complex (Atx2-Not1 repressor complex) via the me31B-dependent association with Not1 to promote Not1-dependent post-transcriptional gene silencing and support high-amplitude circadian rhythms in a per-independent manner (PubMed:28388438). Regulates actin filament formation, though it does not directly assemble with actin filaments (PubMed:12524342). Required for oocyte specification and oocyte positioning in the female germline (PubMed:12524342). Also required for normal eye development and bristle morphology (PubMed:12524342). Homodimer (PubMed:28388438). In the circadian pacemaker neurons, core component of the Atx2-tyf activator complex composed of at least Atx2, tyf, pAbp, Lsm12a (PubMed:28388438). In the circadian pacemaker neurons, also a core component of the Atx2-Not1 repressor complex composed of at least Atx2, tyf, pAbp, me31B (PubMed:28388438). Interacts (via PAM2 motif) with pAbp (PubMed:28388438). Interacts (via N-terminus) with tyf independently of pAbp (PubMed:28388438). Forms a subcomplex composed of Atx2 and pAbP which can associate with the 5' cap of pre-mRNAs independently of tyf, Lsm12a or me31B (PubMed:28388438). Interacts with Lsm12a and me31B (PubMed:28388438). Expressed both maternally and zygotically. Zygotic expression is seen in third larval instar, pupae, and adults. The PAM2 motif, and therefore interaction with pAbp, is essential for binding to the 5' cap of pre-mRNAs. Partially edited. Target of Adar. Second instar larvae lethal. Belongs to the ataxin-2 family. Extended N-terminus. Potential poly-A sequence.