Figure 4. The catalytic activity of Naa50/San is essential for viability and normal mitosis.

A wild type (g(san^wt)), but not a catalytically dead-version (g(san^{R84A Y124F})) of a genomic construct that encodes Naa50/San, was able to rescue the chromosome segregation defects of syncytial blastoderm embryos mutant for san³ (maternal mutants)⁴⁰ (A–D’), the fertility of females whose germ line was mutant for san (E), and the adult viability of zygotic mutants of san (F). Loss of Naa50/San (San^{R84A Y124F}) mutant protein Nt-Ac catalytic activity is shown in Fig. 5B. (A–D’) All panels show syncytial blastoderm embryos. Control wild type (A,A’), san mutant (san³) (B,B’), san mutant with a wild type genomic construct (san³ + g(san^wt)) (C,C’), and san mutant with a catalytically dead genomic construct (san³ + g(san^{R84A Y124F})) (D,D’). Both wild type (g(san^wt)) and catalytically dead genomic constructs (g(san^{R84A Y124F})) contained the gene endogenous minimal promoter and were integrated in the same attP2 site. All embryos were stained for DNA (blue) and pSer10 Histone H3 (green). (E) Embryonic hatching of fertilized eggs laid by females whose germ line was wild type (control), mutant for san with a wild type genomic construct (san³ + g(san^wt)), mutant for san with a catalytically dead genomic construct (san³ + g(san^{R84A Y124F})), and mutant for san (san³) was, respectively, 91.1% ± 5.6 (n = 6434), 85.1% ± 1.6 (n = 5941), 13.5% ± 2.4 (n = 5395), and 0.5% ± 0.7 (n = 762). (F) A genomic construct carrying a wild type copy of san efficiently rescued the zygotic lethality of two loss-of-function alleles of san⁴⁰ (adult viability: san mutant [san³/san⁴] = 0% (n = 294, adult flies); san mutant + g(san^wt) [san³/san⁴; g(san^wt)/+] = 29% ± 1 (n = 328, adult flies; full complementation should correspond to 33% of total Drosophila flies (dashed line)). A genomic construct carrying a catalytically dead allele of san g(san^{R84A Y124F}) failed to rescue the zygotic lethality of two loss-of-function alleles of san (adult viability: san mutant [san³/san⁴] = 0% (n = 294, adult flies); san mutant + g(san^{R84A Y124F}) [san³/san⁴; g(san^{R84A Y124F})/+] = 0% (n = 148, adult flies; full complementation should correspond to 33% of total Drosophila flies). For more experimental detail see Supplementary Table 3.