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	Figure 2. xlADAR1 localizes to the nascent RNP matrix and is specifically enriched on a special loop on bivalent no. 3. LBCs were prepared from oocytes expressing myc-tagged ADAR1.1. (a–d) Normal LBC and (e–f) bivalent no. 3. (a and e) DIC image, (b and f) DAPI staining, (c and g) localization of endogenous ADAR1 detected with SAT4 antiserum in the rhodamine channel and (d and h) localization of myc-tagged ADAR1.1 detected with mAb 9E10 in the fluorescein channel. Endogenous and ectopically expressed ADAR1 is localized to LBC loops. (g and h) A special loop on bivalent no. 3 is enriched for endogenous (g) and ectopically expressed ADAR1 (h). The special loop is marked by arrows. Faint background signals can be seen on nucleoli (N) or snurposomes (S) by staining with SAT4 antiserum that is not seen with myc-tagged ADAR1.1. Bar, 10 μm.
	Figure 3. Localization of ADAR1 to LBC loops is RNA dependent. Staining of bivalent no. 3 with SAT4 antiserum. (a, d, g, j, and m) DIC image, (b, e, h, k, and n) DAPI staining, and (c, f, i, l, and o) staining with Sat4 in the fluorescein channel. (a–c) ADAR1 is localized to LBC loops and is specifically enriched on a special loop. (d–f) Staining with Sat4 can be blocked by ADAR1 peptide. (f) SAT signal is almost completely diminished when the antiserum was blocked with ADAR1 peptide originally used for the immunization. (g–i) SAT staining is sensitive to RNAse treatment. LBCs were digested with RNAse before staining with Sat4 antiserum. (g) The loops appear “stripped” after RNAse treatment, and (i) no signal can be observed in the fluorescein channel. (j–l) Treatment with actinomycin D inhibits transcription and diminishes staining of regular loops but not of the special loop on bivalent no. 3. (j) DIC image of bivalent no. 3 prepared from an oocyte after incubation in AMD. The chromosomal axes is condensed and shows no transcriptionally active loops. Also nucleoli (N) change their morphology. (k) The condensed, shortened chromosomal axes is well stained with DAPI. The position of the special loop forming a “double loop bridge” is seen by the interrupted DAPI staining of the chromosomal axes on both homologues (arrowhead). (l) As transcription is inhibited no ADAR1 staining can be observed. Only the special loop is still brilliantly labeled by SAT4 antiserum. (m–o) Injection of an unrelated oligonucleotide temporarily inhibits transcription but does not affect ADAR1 localization on the special loop on bivalent no. 3. (m) DIC image of bivalent no. 3 prepared from an oocyte 24 h after injection of an oligonucleotide. The presence of loops on the chromosome indicates that transcription has already resumed. (n) DAPI image of the same region. (o) ADAR1 can be detected on most transcripts and on the special loop by staining with SAT4 antiserum. Note: Shortly after injection of the oligo transcription seizes and no ADAR1 staining can be detected on regular loops (not shown). However, staining of the brilliantly labeling loop is not affected by this treatment. Bars, 10 μm.
	Figure 4. Double staining of the special loop on bivalent no. 3 with various antibodies and SAT antiserum. (a, d, g, and j) DIC images, (b, e, h, and k) fluorescein channel, and (c, f, i, and l) staining with SAT4 antiserum in the rhodamine channel. Arrows mark the position of the special loop. (a–c) Staining with mAbH14 (b) shows the presence of RNA Pol-II on all regular loops as a fine signal seen in the center of each loop. However, Pol-II is absent from the special loop which is brilliantly labeled by SAT4 antiserum (c). (d–f) Staining with mAb K121 indicates the presence of 3mG snRNP cap structures on the special loop (e) which is also labeled with SAT4 antiserum (f). (g–i) mAb Y12 stains regular loops and the special loop indicating the presence of Sm proteins on the special loop (h). (j–l) The SR splicing factor SC35 can also be found on the special loop (k). Bar, 10 μm.
	Figure 5. Splicing is not required for ADAR1 localization. (a and d) DIC images, (b and e) DAPI staining, and (c and f) ADAR1 localization detected by staining with SAT4 antiserum in the fluorescein channel. (a–c) Staining of bivalent no. 3 from an untreated oocyte shows localization of ADAR1 on the RNP matrix of regular loops and on the special loop. (d–f) 24 h after injection of the U2b oligo transcription has resumed giving rise to prominent loops (d). (f) Staining with SAT4 antiserum shows the presence of ADAR1 on the loop matrix and on the special loop on bivalent no. 3. Bar, 10 μm.
	Figure 7. (a) Schematic representation of deletion constructs used in this study. The peptide repeats (left striped box), the ZBD (black box), the dsRBDs (right striped box) and the deamination domain (gray box) are indicated. ΔREP deletes the NH2-terminal peptide repeats from ADAR1.1 leaving a single, COOH-terminal myc tag. ΔZBD deletes a longer portion from the NH2 terminus of ADAR1.1 including the putative Z-DNA binding domain and one of two putative NLSs. ADAR1.2 does not contain the peptide repeats and is only myc-tagged at its COOH terminus. An artificial AUG codon was introduced at the beginning of the cDNA. (b) Western blot of oocyte nuclei (GV) and cytoplasms (Cytopl.) of uninjected oocytes (−) and of oocytes expressing myc-tagged ADAR1 versions. All myc-tagged ADAR1 versions express well and accumulate in the nucleus. Cytoplasmic signals are seen 24 h after injection but diminish over time as the protein is transported to the nucleus. (c) ADAR1 undergoes NH2-terminal proteolytic cleavage. Western blot of oocyte nuclei (GV) and cytoplasms (Cytopl.) of uninjected (−) or injected oocytes expressing ADAR1.1 myc tagged at its COOH terminus (C), COOH and NH2 terminus (NC) or NH2 terminus only (N). In the cytoplasm full-length versions (180 to 190 kD) of all three constructs can be easily detected (upper two arrowheads). A smaller (150 kD) breakdown product can only be detected for the two versions carrying a COOH-terminal myc-tag (lower arrowhead). In the nucleus (GV) the breakdown product is the most prominent form found 24 h after injection. However, also the full-length versions can be detected in the nucleus. If the myc-tag is only present at the NH2 terminus (N) only full-length protein can be detected, indicating that the NH2 terminus undergoes proteolytic cleavage.
	Figure 6. In situ localization of ADAR1.2 and ADAR1.1 deletions. (a, e, and i) DIC image, (b, f, and j) DAPI staining, (c, g, and k) localization of myc-tagged ADAR1 variants as seen in the fluorescein channel, and (d, h, l) localization of endogenous ADAR1 as seen after staining with SAT4 antiserum in the rhodamine channel. (a–d) myc-tagged ADAR1.2 localizes like ADAR1.1 to regular loops and to the special loop on bivalent no. 3. (c) the localization of myc-tagged ADAR1.2 and (d) endogenous protein is virtually identical. (e–h) The NH2-terminal peptide repeats found in ADAR1.1 are not required for localization of the protein. (g) myc-tagged ΔREP construct localizes to nascent transcripts and to the special loop on bivalent no. 3. (i–l) Construct ΔZBD, deleting the NH2-terminal end of ADAR1.1 including a putative Z-DNA binding domain and one putative NLS, shows wild-type-like in situ localization. (k) myc-tagged ΔZBD construct (l) counterstaining with Sat4 antiserum. Bar, 10 μm.

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