Publish or perish needs to end.

After a bit of digging - it looks like it's done to sharpen features as one of the standard steps in producing these images. Where there are rotational symmetries in the things they're looking at, they focus on the smallest unit, and then rotate accordingly. If you had a trilateral symmetry, or hexagonal structure, they'd rotate 3 or 6 times around the center.

You're not getting a real image of the thing, but apparently it's got data from those other segments mixed in with the rotations, so you're getting a kind of idealized structure, to make the details being studied pop out, but if you have some sort of significant deviation, damage, or non symmetric feature it'll show up as well.

It's called "imposed symmetry" https://discuss.cryosparc.com/t/what-is-actually-occuring-wh...

Neat stuff, cool thing to catch!

A different paper, this figure shows a number of cryo-em images, including a simulation, and they all show the same degree of pattern symmetry https://www.researchgate.net/figure/Central-sections-through...

First figure in this third paper also shows symmetry of small patterns https://journals.asm.org/doi/10.1128/jvi.00990-22

I believe that Eukaryotes then from Archae.