Lamins are the major constituent of the nuclear lamina, a protein meshwork underlying the inner nuclear membrane. Nuclear lamins are type V intermediate filaments that assemble into ~3.5 nm thick filaments. To date, only the conditions for the
in vitro
assembly of
Caenorhabditis elegans
lamin (
Ce
-lamin) are known. Here, we investigated the assembly of
Ce
-lamin filaments by cryo-electron microscopy and tomography. We show that
Ce
-lamin is composed of ~3.5 nm protofilaments that further interact
in vitro
and are often seen as 6–8 nm thick filaments. We show that the assembly of lamin filaments is undisturbed by the removal of flexible domains,
that is,
the intrinsically unstructured head and tail domains. In contrast, much of the coiled-coil domains are scaffold elements that are essential for filament assembly. Moreover, our results suggest that
Ce
-lamin helix 1A has a minor scaffolding role but is important to the lateral assembly regulation of lamin protofilaments.