The 39S ribosomal protein appears to be a subunit of one of the larger mitochondrial 66S or 70S units [1]. Under conditions of ethanol-stress in rats the larger subunit is largely dissociated into its smaller components [2]. In E. coli, in the absence of the enzyme pseudouridine synthase (RluD) synthase, there is an accumulation of 50S and 30S subunits and the appearance of abnormal particles (62S and 39S), with concomitant loss of 70S ribosomes [2].

1: Differential effects of chronic ethanol consumption on hepatic mitochondrial and cytoplasmic ribosomes. Cahill A, Baio DL, Ivester P, Cunningham CC; Alcohol Clin Exp Res. 1996;20:1362-1367. PMID:8947311

2: The pseudouridine synthase RluD is required for normal ribosome assembly and function in Escherichia coli. Gutgsell NS, Deutscher MP, Ofengand J; RNA. 2005;11:1141-1152. PMID:15928344